The alligator and its allies

A. M. (Albert Moore) Reese

Transcriber’s Notes

Texts printed in italics and bold face in the source document have been transcribed between _underscores_ and =equal signs=. Small capitals have been replaced with ALL CAPITALS.

More Transcriber’s Notes may be found at the end of this text.

[Illustration:

ALLIGATOR MISSISSIPPIENSIS. (After Ditmars.)

(Reproduced by Permission of Doubleday, Page & Company.)]

The Alligator and Its Allies

By Albert M. Reese, Ph.D. Professor of Zoölogy in West Virginia University Author of “An Introduction to Vertebrate Embryology”

_With 62 Figures and 28 Plates_

G. P. Putnam’s Sons New York and London The Knickerbocker Press 1915

Copyright, 1915 By Albert M. Reese

The Knickerbocker Press, New York

Preface

The purpose of this volume is to bring together, in convenient form for the use of students of zoölogy, some of the more important details of the biology, anatomy, and development of the Crocodilia. For obvious reasons the American Alligator is the species chiefly used.

In the first chapter the discussion of the alligator is largely the result of the personal observations of the author; the facts in regard to the less familiar forms are taken from Ditmars and others. The description of the skeleton, with the exception of short quotations from Reynolds, is the author’s.

The chapter on the muscular system is a translation from Bronn’s _Thierreich_, and the author has not verified the descriptions of that writer.

The description of the nervous system is partly the author’s and partly taken from Bronn and others.

The chapters on the digestive, urogenital, respiratory, and vascular systems are practically all from descriptions by the author.

The chapter on “The Development of the Alligator” is a reprint, with slight alterations, of the paper of that title published for the author by the Smithsonian Institution.

The bibliography, while not complete, will be found to contain most of the important works dealing with this group of reptiles.

The author is grateful to Mr. Raymond L. Ditmars and to his publishers, Messrs. Doubleday, Page & Co., and Messrs. Sturgis & Walton, for the use of a number of plates; to the Macmillan Company and to the United States Bureau of Fish and Fisheries for the same privilege; to the National Museum for photographs of the skull of the gavial; and to the Smithsonian Institution for the use of the plates from researches published by them and included herein.

Proper acknowledgment is made, under each borrowed figure, to the author from whom it is taken.

MORGANTOWN, W. VA. _May 1, 1915._

Chapter I The Biology Of The Crocodilia 1

Chapter II The Skeleton 46

Chapter III The Muscles 90

Chapter IV The Nervous System 131

Chapter V The Digestive System 150

Chapter VI The Urogenital System 192

Chapter VII The Respiratory System 197

Chapter VIII The Vascular System 201

Chapter IX The Development Of The Alligator 226

Bibliography 343

Index 349

Illustrations

Page

ALLIGATOR MISSISSIPPIENSIS. (In color.) _Frontispiece_

Figure

A. Skull Of Belodon 5

1. Map Showing The Present Distribution Of Crocodilia 6

2. HEADS OF AMERICAN ALLIGATOR AND CROCODILE _Facing_ 7

3. ALLIGATOR JOE IN THE EVERGLADES _Facing_ 10

4. ALLIGATOR HUNTER IN THE OKEFINOKEE _Facing_ 10

5. NEST OF C. POROSUS _Facing_ 21

6. JACKSON SLOUGH _Facing_ 21

7. A TYPICAL ALLIGATOR HOLE _Facing_ 23

8. ALLIGATOR NEST, MADE CHIEFLY OF GRASS _Facing_ 25

9. ALLIGATOR NEST, MADE CHIEFLY OF FLAGS _Facing_ 27

10. TWO SPECIES OF CAIMAN: BROAD-NOSED CAIMAN, SPECTACLED CAIMAN _Facing_ 35

11. TWO AFRICAN CROCODILES: NILE CROCODILE, WEST AFRICAN CROCODILE _Facing_ 39

12. SALT WATER CROCODILE _Facing_ 41

13. SKULL OF GAVIAL, VENTRAL VIEW _Facing_ 43

14. SKULL OF GAVIAL, LATERAL VIEW _Facing_ 43

15. ALLIGATOR SKINS _Facing_ 46

16. Entire Skeleton Of Crocodile 50

17. First Four Cervical Vertebræ Of Crocodile 52

18. Thoracic And Sacral Vertebræ Of Crocodile 55

19. DORSAL VIEW OF SKULL OF ALLIGATOR _Facing_ 60

20. VENTRAL VIEW OF SKULL OF ALLIGATOR _Facing_ 63

20A. LONGITUDINAL SECTION OF TOOTH OF CROCODILE _Facing_ 66

21. Lateral View Of Skull Of Alligator 69

22. POSTERIOR VIEW OF SKULL OF ALLIGATOR _Facing_ 70

23. Sagittal Section Of The Skull Of Alligator 71

24. DORSAL VIEW OF LOWER JAW OF ALLIGATOR _Facing_ 74

25. The Hyoid Apparatus 77

26. The Sternum And The Associated Membrane Bones 79

27. The Pectoral Girdle And Anterior Limb 82

28. The Pelvis And Sacrum 85

29. The Posterior Limb 87

I. PLATE I. THE SHOULDER MUSCLES _Following_ 130

II. PLATE II. THE MUSCLES OF THE ANTERIOR REGION _Following_ 130

III. PLATE III. THE MUSCLES OF THE POSTERIOR REGION _Following_ 130

IV. PLATE IV. THE MUSCLES OF THE POSTERIOR REGION _Following_ 130

V. PLATE V. THE MUSCLES OF THE POSTERIOR REGION _Following_ 130

30. THE BRAIN OF THE ALLIGATOR _Facing_ 132

31. The Brachial Plexus Of C. Acutus 140

32. The Crural Plexus Of A. Mississippiensis 142

33. INTERIOR OF THE MOUTH OF THE ALLIGATOR _Facing_ 151

34. The Digestive System Of The Alligator 152

35. Outline Of The Digestive Tract Of The Alligator 158

36. Covering Of The Anterior Region Of The Tongue 160

37. Covering Of The Posterior Region Of The Tongue 161

38. Gland From The Posterior Region Of The Tongue 162

39. Gland From The Posterior Region Of The Tongue 164

40. Covering Of The Roof Of The Mouth 166

41. Transsection Of The Anterior Region Of The œSophagus 169

42. Transsection Of The Posterior Region Of The œSophagus 170

43. Epithelium Of Anterior Region Of œSophagus 172

44. Epithelium Of Anterior Region Of œSophagus 173

45. Transsection Of Wall Of Pyloric Stomach 176

46. Glands Of Fundus Of Stomach 177

47. Transsection Of Wall Of Anterior Region Of Small Intestine 181

48. Transsection Of Wall Of Middle Region Of Small Intestine 182

49. Transsection Of Wall Of Posterior Region Of Small Intestine 183

50. Mucosa Of The Anterior Region Of Small Intestine 184

51. Transsection Of The Wall Of The Middle Region Of The Small Intestine 185

52. Transsection Of The Wall Of The Anterior Region Of The Rectum 186

53. Epithelium Of The Anterior Region Of The Rectum 187

54. Female Urogenital System Of Alligator 193

55. MALE UROGENITAL SYSTEM OF ALLIGATOR _Facing_ 195

56. MALE ORGAN OF ALLIGATOR _Facing_ 195

57. Respiratory Organs Of Alligator 198

58. HEART OF ALLIGATOR _Facing_ 202

59. Veins Of The Posterior Region Of Alligator 204

60. Veins Of The Anterior Region Of The Alligator 209

61. Arteries Of The Posterior Region Of The Alligator 213

62. Arteries Of The Anterior Region Of The Alligator 215

VI.-XXVIII. PLATES VI TO XXVIII. A SERIES OF FIGURES TO ILLUSTRATE THE DEVELOPMENT OF THE AMERICAN ALLIGATOR _Following_ 342

The Alligator And Its Allies

Chapter I

The Biology Of The Crocodilia

Classification

As in most groups of animals, there is considerable difference of opinion as to the proper classification of the Crocodilia.

One of the older textbooks (Claus and Sedgwick) divides the order Crocodilia into three sub-orders: the _Teleosauria_, _Steneosauria_, and _Procœlia_, the last only being represented by living forms. The Procœlia or Crocodilia proper are divided into three families,--the _Crocodilidæ_, the _Alligatoridæ_ (including the caiman as well as the alligator), and the _Gavialidæ_.

This division into families seems to be based mainly on the shape of the head, or, at any rate, it throws those forms together that have heads of the same outline.

It is this outline of the head that Ditmars (_Reptiles of the World_) uses in classifying the Crocodilia, which, he says, are all included in the single family--_Crocodilidæ_. The following list, taken from his _Reptiles of the World_ (pp. 68-69), will give a clear idea of the number, distribution, and maximum size of the members of the order Crocodilia. More will be said of some of the members of this list later.

[1] These species are exceptions in their genus. The snout is blunt like that of the genus _Alligator_.

[2] Alleged to grow to this size by competent observers.

Gadow in the _Cambridge Natural History_ (p. 450) agrees with Boulanger in believing that the recent Crocodilia cannot be separated into different families, yet he describes seven families of Crocodilia, two of which, the _Gavialidæ_ and _Crocodilidæ_, include the living members of the order; the former includes the gavials, of course, and the latter the crocodiles, alligators, and caimans.

Though “doctors disagree” thus in regard to the scientific classification of this small group of animals, this fact does not in the least diminish the intense interest in the individual members of the order.

Ancestry

Although the huge dragon-like dinosaurs or “terrible reptiles,” some of which were probably more than one hundred feet long, became extinct during the Mesozoic epoch, perhaps millions of years before man made his appearance upon earth, we have one group of reptiles still living in certain parts of the earth of which the Mesozoic lords of creation need not feel ashamed. While most of the living Crocodilia are mere pigmies in size, compared to the Atlantosaurus, there are a few representatives of the living group, to be discussed later, that are said to reach a length of thirty feet, which length makes pigmies, in turn, of most of the other living reptiles.

Considering the extinct as well as the living Crocodilia, Gadow says it is very difficult to separate them from the Dinosauria. In the Mesozoic Crocodilia the fore limbs were much shorter and weaker than the hind limbs, as was often the case with the dinosaurs; they were almost entirely marine, but gave indications of descent from terrestrial forms.

Various facts point, thinks Gadow, “to some Theropodous Dinosaurian stock of which the Crocodilia may well form an aquatic, further developed branch” (_Cambridge Natural History_, p. 432).

[Illustration:

Skull of =Belodon=. A, from above; B, from below. _A_, orbit; _Bo_, basi-occipital; _Ch_, internal nares; _D_, pre-orbital fossa; _Exo._ exoccipital; _Fr._ frontal; _Ju._ jugal; _La._ lacrymal; _Mx._ maxilla; _Na._ nasal; _Pa._ parietal; _Pl._ palatine; _Pmx._ pre-maxilla; _Por._ post-orbital; _Prf._ pre-frontal; _Pt._ pterygoid; _Qu._ quadrate; _S_, lateral temporal fossa; _S′_, superior temporal fossa; _Sq._ squamosal; _Vo._ vomer. (From Zittel.)

Fig. A. A Triassic Ancestor Of The Crocodilia.

From Parker & Haswell, _Textbook of Zoölogy_.]

The direct ancestors of the Crocodilia, Gadow says, are still unknown.

Geographical Distribution

As will be seen by examination of the table (p. 2) from Ditmars, and of Figure 1, the recent Crocodilia are found in all of the great continental areas except Europe; mainly in the tropical or subtropical regions.

[Illustration: FIG. 1. MAP SHOWING PRESENT DISTRIBUTION OF CROCODILIA.

(After Gadow.)]

The alligator is found in the southwestern United States and in China.

The crocodile is the most numerous in species and is the most widely distributed of the group. It is especially characteristic of Africa and Madagascar, but is found also in Florida, Mexico, Central and South America, the West Indies, South Asia, the East Indies, and Australia.

The gavial is found in India and some of the islands of the Orient, especially Borneo and Sumatra.

The caiman occurs in southern Mexico, Central and South America.

[Illustration: FIG. 2. HEADS OF AMERICAN ALLIGATOR AND AMERICAN CROCODILE; ALLIGATOR ON LEFT. (After Ditmars.)

(Reproduced by Permission of Sturgis & Walton Co.)]

The distribution of individual forms will be mentioned again when they are discussed in detail.

Alligator Mississippiensis

Since this animal, generally known as the American or the Florida alligator (formerly _A. lucius_), is the one upon which most of the facts of this book are based, it will be discussed first.

At this point it may be well to answer the question that is sure to be asked by someone early in any conversation upon the Crocodilia. The writer, and doubtless every other zoölogist, has been asked countless times, “What is the difference between an alligator and a crocodile?” As a matter of fact there is, perhaps, no absolute distinction between the two groups, but there are certain features that make it easy to distinguish, say, between the American alligator and the American crocodile.

The most striking difference is in the outline of the head; the alligator has a broad, rounded snout, while that of the crocodile is narrower and more pointed (Fig. 2). Again, in the crocodile the fourth tooth from the front projects slightly outwards and fits into a notch in the side of the upper jaw, while in the alligator (also in the caiman) the corresponding tooth on each side fits into a socket in the upper jaw and hence is hidden, except in some old animals with very long teeth, in which it may pierce the upper jaw and show from above. According to Ditmars, the crocodile has, as a rule, larger and more exposed teeth than the alligator. Finally, as will be brought out later, the crocodile is usually more quick and active, and also more vicious, than the alligator.

Very young alligators are nearly black, with distinct, yellow cross bands; as they grow older these markings become less distinct until in maturity the animals are of a uniform gray or dirty black color.

_Habitat._ The American alligator is found in the rivers and swamps of the Southern States, from the southern part of North Carolina to the Rio Grande, though Florida is usually thought of as being the region in which they particularly abound. Years ago, before the rifle of the ubiquitous tourist and so-called sportsman had gotten in its deadly work, the alligators were probably very abundant in the Southern States; but they have been so ruthlessly destroyed by native hunters for their skins, and by others for mere wanton sport, that one may travel, perhaps, for days along the rivers of the South without seeing a single ’gator.

The account quoted by Clarke from Bartram’s travels of more than one hundred years ago, while probably exaggerated, gives an idea of the abundance of the alligators at that time: “The rivers at this place from shore to shore, and perhaps near a half mile above and below me, appeared to be one solid bank of fish of various kinds, pushing through the narrow pass of San Juans into the little lake on their return down the river, and the alligators were in such incredible numbers, and so close together from shore to shore, that it would have been easy to have walked across their heads, had the animals been harmless.” At the present time it is usually necessary to travel far from the usual routes of the Northern tourists to find alligators in any abundance.

At Palm Beach, Florida, lived, a few years ago, and probably still lives, a well-known hunter and guide, “Alligator Joe.” Just what nationality he may be is difficult to determine, but that he knows that trackless waste, the Everglades, at least in the region of Palm Beach, is evident. He has an “alligator farm” near the great hotels of that famous winter resort, at which he keeps, or did a few years ago, a large number of alligators of all sizes, as well as a number of crocodiles. For a consideration (by no means a modest one) he would take out a party of tourists for a day into the Everglades, guaranteeing that he would find an alligator for them to shoot. It was rumored by the natives that an accomplice was always sent ahead to free the alligator at the psychological moment, after the hunters had been paddled by a devious course to the selected spot, but whether this were true or not the writer was not able to determine. It is true, however, that he and the writer paddled in a rather graceful canoe, dug out of a single cypress log, and waded through the Everglades for several days, searching for alligator eggs, and that we found only one nest and saw only one or two alligators (Fig. 3).

Doubtless in more remote parts of the Everglades the alligators are much more numerous.

During another summer the writer, with a guide, penetrated the very center of the State, to the region southeast of Lake Kissimmee, forty miles from the nearest railroad; here the alligators, and in consequence their nests, are fairly abundant, though the native hunters are, even in this remote region, rapidly thinning their ranks.

A still greater number of alligators was found, the following summer, in the Okefinokee Swamp in southern Georgia. In the center of this great waste, ten miles or more from dry land, nearly one hundred alligators, ranging from about four to eight feet in length, were killed within a week by a small party of native hunters with whom the writer was traveling (Fig. 4).

Whether this wholesale destruction by sportsman and native hunter will eventually exterminate our giant reptile, as has been the case with the buffalo and other game animals, it is impossible to say. Unless the Everglades and the Okefinokee are largely drained it seems probable that a few alligators will always remain in the most inaccessible regions.

[Illustration: FIG. 3. ALLIGATOR JOE IN THE EVERGLADES.

(From a Photograph by the Author.)]

[Illustration: FIG. 4. ALLIGATOR HUNTER IN THE OKEFINOKEE.

(From a Photograph by the Author.)]

The collection of eggs for sale and for hatching purposes, as well as their destruction for food by bears and other animals, will also tend towards the annihilation of the species in the course of time. The economic importance of the alligator will be discussed later.

While in the old days, as has been said, the alligator was common in the larger rivers and lakes, and may even have ventured short distances into salt water, he must now frequently be satisfied to hide his great body in a “’gator hole” that is scarcely more than a puddle. These “holes” (Fig. 7) are common in central Florida and are sometimes scarcely large enough to allow the alligator to dive into them to seek the underground cave in which he hides. It is on the edge of such a hole that the nest is built, as will be described later.

Often from a small swamp or slough alligator “trails” lead off in different directions. These trails are narrow, winding gullies such as might be made by cattle in a damp pasture. If followed from the main slough the trail will usually be found to end in a “hole,” in which an alligator will probably be found (Fig. 7). In a great swamp like the Everglades or the Okefinokee such holes would naturally not be found.

On one side of the hole is usually a smooth place where the vegetation is worn away; it is here that the ’gator “pulls out” to sleep in the sun; and wary must the hunter be to approach within sight of the animal before being seen or heard by him. At the first alarm he slides quietly or plunges quickly into the muddy water, and the hunter must wait long if he expects to see the ’gator come to the surface.

The opening of the cave is always below the surface of the water, but it is possible that there may be a subterranean chamber that is not completely filled with water. How the animal is gotten from his cave will be described later. According to some writers the alligator retires to his cave to hibernate during the cooler winter months. This is possibly true in the more northerly limits of his range. It is well known that if kept in cool water the alligator will lie dormant and refuse all food for months at a time. The writer has had young alligators in captivity, under these conditions, that refused food from late in the autumn until nearly the first of April.

The proprietor of one of the largest alligator farms in the country says: “Our alligators stop eating the first week in October and do not begin to eat until the latter part of April. We have experimented with our stock to see if we could get them to eat in the winter, and found that by keeping the water in the tanks at a certain temperature they would eat, but we found out that the warm water would make their bowels move, and that they would not eat enough to keep themselves up, as in the summer, and as a result they would become very poor and thin, so we do not force them to eat any more.” The effect upon the growth of an animal of these two methods of feeding will be noted later when the age and rate of growth are discussed. The same writer says, in answer to a question about hibernation: “In their wild state they go into their dens under water and remain dormant all winter.” Whether this statement is the result of actual observation the writer is not able to say, but, judging by some other statements from the same source, it is probably from hearsay. The writer, having visited the alligator haunts only in late spring and summer, has had no opportunity of studying the habits of the animal in its natural habitat during the winter season. During the heat of summer the animal does not seek the sun as he is said to do during cooler weather, but spends more time on the bank at night and during the cooler parts of the day.

That he sometimes wanders over dry land, perhaps going from hole to hole, is evident from the tracks that are sometimes seen crossing a dusty road or path. These trails are easily recognized by the clawed footprints with a line, made by the dragging tail, between them. Although most awkward on land, he can, if necessary, move very quickly. It is, however, in the water that he shows to best advantage; he is an active, powerful swimmer, his tail being used as a propeller as in the fishes. When swimming actively the legs are held close against the body in order that they may retard the animal’s motion as little as possible. While swimming in a leisurely way the top of the head is at the surface of the water, perhaps just the nostrils and eyes projecting above the surface, so that the size of the animal can be estimated by the distance between these projecting points. One afternoon the writer and a guide, while paddling along an old canal that was dug years ago into the Okefinokee Swamp, were preceded for perhaps half a mile by a large alligator that swam just fast enough to keep out of our reach until he came to the place where he wanted to turn off into the swamp.

Although so awkward on land, the alligator is said to be able to defend himself very effectively with his tail, which he sweeps from side to side with sufficient force, in the case of a large specimen, to knock a man off his feet. Although the writer has seen captured and helped to capture alive several alligators up to eight feet in length he has never seen this vigorous use of the tail as a weapon of defense.

While the alligator, like most other wild animals, will doubtless defend itself when cornered, it will always flee from man if possible, and the writer has frequently waded and swam in ponds and lakes where alligators lived without the least fear of attack. This might not have been possible years ago when the animals were more numerous and had not been intimidated by man and his weapons.

_Food._ The food of the adult alligator consists of fishes, birds, mammals, and possibly smaller individuals of its own species. The young eat small fish, frogs, insects, or worms.

If the animal be too large to swallow whole it is shaken and torn, the shaking being so vigorous that, according to Ditmars, the entrails of the prey may be thrown to a distance of twenty feet or more. Should two alligators seize the same prey at the same time they whirl about in opposite directions so violently that the prey is torn apart. This action may be illustrated by giving two small captive alligators a piece of tough meat; they hold on with bulldog tenacity, and each, folding its legs close to its body, will use its tail like a propeller until the animal whirls around with remarkable speed. The commotion that two ten-foot alligators would cause when thus struggling can easily be imagined. That a large alligator, if it tried, could easily drag under the water and drown a man or possibly a much larger animal is evident.

While the alligator has a valve-like fold of skin in its throat that enables it to open its mouth and crush its prey under water, it is said that it must raise its head above water in order to swallow its food. A young alligator on land will usually throw back its head when trying to swallow a large piece of meat, so that it may be simply this motion that brings the head of the alligator above the surface of the water.

Ditmars thus describes the fate of a dog that approached too near a very large alligator: “As a dog, weighing about fifty pounds, unwarily approached the edge of this creature’s tank, it was suddenly grasped and before completing its first yelp of terror was dragged beneath the surface. A few minutes later the twelve-foot saurian appeared at the top, holding the dead canine in its jaws. The dog was shifted about, amid the sound of breaking bones, and swallowed head first, and entire, after a few gulps.”

_Size and Growth._ Although, years ago, alligators of fifteen feet length may have been common in favorable localities in the South, it is probable that few if any such monsters now exist. A twelve-foot alligator, owing to its great girth, is a huge animal and but few of this size are to be found in captivity. The largest specimen the writer has ever seen is the one in the Bronx Zoo, which is barely thirteen feet in length. At hatching the alligator is about eight inches in length.

Clarke (17) says: “The largest specimen I saw measured twelve feet in length; and none of the many hunters and natives of Florida I have met have seen any longer than thirteen feet. All the hunters agree that it is only the males that acquire the great size; no one had ever seen a female that measured over eight feet, and the majority are not over seven. The male has a heavier, more powerful head, and during the breeding season especially is more brilliantly colored.”

It is a very common belief, even among those who should be most familiar with their habits, that the growth of the alligator is remarkably slow, so that a large specimen may be described by the exhibitor as more than a century old. The same dealer in alligators quoted above says upon this subject: “You can figure about two inches a year to their growth.” He also says: “We judge that an alligator about twenty-five to thirty years old will breed.” Even scientific writers of reputation have not been free from this error in their writings. That the alligator may live to an extreme age, as seems to be true of some of the tortoises, is quite possible, and it is probable that after reaching a length of twelve or fifteen feet the growth is very slow.

In captivity, when kept in warm water and other favorable conditions, the alligator will grow, according to measurements taken at the New York Zoölogical Park, at the rate of about one foot a year, for about the first ten years. Under unfavorable conditions the growth may be exceedingly slow. Under favorable conditions in nature the rate of growth may exceed that given above.

Instead of requiring twenty-five to thirty years to reach sexual maturity, as quoted above, it is likely that the female may lay eggs at five to ten years, though such a fact is difficult to determine of animals in their native haunts.

_Voice._ The alligator, unlike most other members of its class, the _Ophidia_, _Chelonia_, and _Lacertilia_, has a voice, which, in an adult bull, may be heard for a mile or more. This bellowing is difficult to describe; it is something between a moan and a roar, and may be to attract the opposite sex or to serve as a challenge to other large animals. It is usually ascribed to the male, but whether confined to him or not the writer is unable to say.

In younger animals the voice is, of course, less deep and in very young individuals it is a squeak or grunt, easily imitated by hunters for the purpose of luring the animals from their hiding places.

_Breeding Habits._ Judging from the statements of native hunters the laying season of the alligator might be thought to be at any time from January to September. As a matter of fact the month of June is the time when most, if not all, of the eggs are laid. S. F. Clarke gives June 9th and June 17th as the limits of the laying season in Florida, but I found at least one nest in which eggs were laid as late as June 26th: no eggs were found before the first date given by Clarke. It seemed quite certain that the laying, during the season in question, had been delayed by an extreme drought that had dried up the smaller swamps and reduced the alligator holes to mere puddles. Nests were found in considerable numbers as early as June 8th, but no eggs were laid in any of them until the end of the dry period which occurred nearly two weeks later. Almost immediately after the occurrence of the rains that filled up the swamps eggs were deposited in all of the nests at about the same time. From the fact that all of these completed nests had stood for so long a time without eggs, and from the fact that all of the eggs from these nests contained embryos in a well-advanced state of development, it seemed evident that the egg-laying had been delayed by the unusually dry weather. Eggs taken directly from the oviducts of an alligator that was killed at this time also contained embryos that had already passed through the earlier stages of development. Thus it was that the earliest stages of development were not obtained during this summer.

It is said that during the mating season, which precedes by some time, of course, the laying season, the males are noisy and quarrelsome, and that they exhibit sexual characteristics of color by which they may be distinguished from the females. Never having been in the alligator country at this season, the writer has made no personal observations along these lines, but from the frequency with which alligators with mutilated or missing members are found it is evident that fierce encounters must sometimes take place, whatever the cause. During June and July, at least, and probably during most of the year, the alligators are very silent, an occasional bellow during the very early morning hours being the only audible evidence that one has that the big reptiles are in the neighborhood. Whatever may be the sexual differences during the mating season, at ordinary times the two sexes are so much alike that I have, on more than one occasion, seen experienced hunters disagree as to the supposed sex of an alligator that had just been killed.

Although I have never seen a nest actually during the process of construction, it is easy to imagine, after the examination of a large number of freshly made nests, what the process must be like.

The alligator, probably the female, as the male, after the mating season, takes no interest whatever in the propagation of his species, selects a slight elevation on or near the bank of the “hole” in which she lives. This elevation is generally, though not always, a sunny spot, and is frequently at the foot of a small tree or clump of bushes. Where the alligator is living in a large swamp she may have to go a considerable distance to find a suitable location for her nest; when her hole is scarcely more than a deep, overgrown puddle, as is often the case in the less swampy regions, she may find a good nesting place within a few feet of her cave. That the female alligator stays in the neighborhood of her nest after she has filled it with eggs seems pretty certain, but that she defends it from the attacks of other animals is extremely doubtful: certainly man is in very little danger when he robs the nest of the alligator, and, according to the statement of reliable hunters, bears are very persistent searchers for and eaters of alligator eggs. Having selected (with how much care it is impossible to say) the location for the nest, the alligator proceeds to collect, probably biting it off with her teeth, a great mass of whatever vegetation happens to be most abundant in that immediate vicinity. This mass of flags or of marsh grass is piled into a conical or rounded heap and is packed down by the builder repeatedly crawling over it.

[Illustration: FIG. 5. A NEST OF C. POROSUS: PALAWAN, P. I.

(From a Photograph by Rowley.)]

[Illustration: FIG. 6.--JACKSON SLOUGH; NEAR LAKE KISSIMMEE, FLORIDA.

In the vicinity of this pond several alligator nests were found, either within a few yards of the edge, or on the banks of smaller “holes” which were connected with the larger pond by narrow “trails.” (From a Photograph by the Author.)]

There is a great deal of variation in the size and form of the different nests, some being two meters or more in diameter and nearly a meter in height, while others are much smaller in diameter and so low as to seem scarcely more than an accidental pile of dead vegetation. It is probable that the nests are under construction for some time, perhaps to give time for the fresh vegetation of which they are composed to ferment and soften, and also for the material to settle into a more compact mass. The compactness of the alligator’s nest was well illustrated one day when the writer used an apparently deserted nest as a vantage ground from which to take a photograph: on opening this nest it was found, after all, to contain eggs, and though some of the eggs were cracked, none of them were badly crushed. This nest although it was so low and flat that it was thought to be one that had been used during some previous season, contained forty-eight eggs, a greater number than was found in any other nest; while in other nests that were twice as large as this one were found less than half as many eggs, showing that there is no relation between the size of the nest and the number of eggs. The average number of eggs per nest, in the twelve nests that were noted, was thirty-one. One observer reported a nest that contained sixty eggs, but this, if true, was a very unusual case. Reports of still larger numbers of eggs in one nest probably refer to crocodiles, which are said to lay one hundred or more eggs in a nest. Although crocodiles may be found in certain parts of Florida, the writer has had no opportunity of observing their nesting habits.

The eggs are laid in the nest without any apparent arrangement. After the nest has been prepared, and has had time to settle properly, the alligator scrapes off the top, and lays the eggs in a hole in the damp, decaying vegetation; the top of the nest is again rounded off, and it is impossible to tell, without examination, whether the nest contains eggs or not.

As to whether the same nest is used for more than one season there is a difference of opinion among alligator hunters, and the writer has had no opportunity of making personal observations.

[Illustration: FIG. 7. A TYPICAL ’GATOR “HOLE.”

Only a few yards across, and surrounded by a dense growth of vegetation. On the far side is seen an opening in the surrounding grass and flags where the ground is worn smooth by the alligator in crawling out of the hole. Under the bank, probably near the place where the alligator “pulls out,” is the deep cave into which the inhabitant of this hole quickly goes on the approach of danger. As this cave may be fifteen or twenty feet deep it is not an easy matter to get the animal out. When a female alligator inhabits such a hole, a nest may often be found within three or four yards of the water, though it is sometimes at a greater distance. Such a hole as this may be connected by narrow, winding “trails” with larger ponds, as noted under Fig. 6. (From a Photograph by the Author.)]

While it is usually stated that the eggs are incubated by the heat of the sun, it is held by some observers that the necessary heat is derived not from the sun but from the decomposition of the vegetable matter of which the nest is composed. Possibly heat may be derived from both of these sources, but it seems likely that the conditions that are especially favorable to normal incubation are moisture and an even, though not necessarily an elevated, temperature. Moisture is certainly a necessary condition, as the porous shell allows such rapid evaporation that the egg is soon killed if allowed to dry. The inside of the nest is always damp, no matter how dry the outside may become under the scorching sun, so that this condition is fully met. The eggs of the Madagascar crocodile, according to Voeltzkow,[3] offer a marked contrast to those of the alligator. Instead of being laid in damp nests of decaying vegetation, they are laid in holes that are dug in the dry sand, and are very sensitive to moisture, the early stages, especially, being soon killed by the least dampness. A crocodile’s nest containing eggs is shown in Figure 5. In this species of crocodile, probably _C. porosus_, the nest resembles that of the Florida alligator. The photograph was taken by Mr. Rowley on the edge of a small lake on the Island of Palawan, P. I.

[3] Voeltzkow, A., “The Biology and Development of the Outer Form of the Madagascar Crocodile,” _Abhandl. Senckberg. Gesell._, Bd. 26, Hft. I.

The daily range of temperature in the Southern swamps is sometimes remarkably great, so that if the eggs were not protected in some way they would often pass through a range of temperature of possibly fifty degrees or more; while in the center of a great mass of damp vegetation they are probably kept at a fairly constant temperature. Unfortunately no thermometer was taken to the swamps, so that no records of the temperatures of alligator nests were obtained, but it was frequently noticed that when, at night or very early in the morning, the hand was thrust deep into the center of an alligator’s nest the vegetation felt decidedly warm, while in the middle of the day, when the surrounding air was, perhaps, fifty degrees (Fahrenheit) warmer than it was just before sunrise, the inside of the same nest felt quite cool. It is probable, then, that the conditions of temperature and moisture in the center of the nest are quite uniform. One lot of eggs that had been sent from Florida to Maryland continued to incubate in an apparently normal way when packed in a box of damp sawdust, the temperature of which was about 80 degrees Fahrenheit. Another lot of eggs continued to incubate, until several young alligators were hatched, in the ordinary incubator, at a temperature of about 95 degrees Fahrenheit.[4]

[4] Reese, A. M., “Artificial Incubation of Alligator Eggs,” _Amer. Nat._, March, 1901, pp. 193-195.

The fact that eggs taken directly from the oviducts of the cold-blooded alligator contain embryos of considerable size seems to indicate that no such elevation of temperature as is necessary with avian eggs is necessary with the eggs of the alligator.

[Illustration: FIG. 8. A TYPICAL ALLIGATOR’S NEST, MADE CHIEFLY OF GRASS.

The guide is feeling for eggs without disturbing the outside of the nest. Being made of the same material as the background, the nest does not stand out very sharply, though in nature the contrast is somewhat more marked, owing to the fact that the surrounding grass is green while the grass of which the nest is built is dead and brown. (From a Photograph by the Author.)]

The complete process of incubation probably extends through a period of about eight weeks, but no accurate observations along this line could be made. For some hours previous to hatching the young alligators make a curious squeaking sound inside the shell, that may be heard for a distance of several yards: this sound may be for the purpose of attracting the attention of the female alligator, who will open the top of the nest in time to allow the just hatched alligators to escape: unless thus rescued, it would seem impossible for the little animals to dig their way out from the center of the closely packed mass of decaying vegetation.

At the time of hatching the alligator is, as already noted, about eight inches in length, and it seems impossible that it should have been contained in so small an egg.

The size of alligator eggs, as might be expected, is subject to considerable variation. In measuring the eggs a pair of brass calipers was used, and the long and short diameters of more than four hundred eggs were obtained. A number of eggs of average size, when weighed in mass on the scales of a country store, gave an average of 2.8 oz. per egg.

There was more variation in the long diameter of eggs than in the short diameter.

The longest egg of all those measured was 85 mm.; the shortest was 65 mm. The widest egg (greatest short diameter) was 50 mm.; the narrowest egg (least short diameter) was 38 mm.

The average long diameter was 73.742 mm.; the average short diameter was 42.588 mm.

The greatest variation in long diameter in any one nest of eggs was 15.5 mm.; the greatest variation in short diameter in the eggs of any one nest was 11 mm.

The average variation in the long diameter of the eggs from the same nest was 11.318 mm.; the average variation in the short diameter of the eggs from the same nest was 5.136 mm.

It will be seen from the above that the average variation in the long diameter of eggs from the same nest is between one sixth and one seventh of the long diameter of the average egg; while the average variation in the short diameter of the eggs from the same nest is less than one eighth of the short diameter of the average egg.

S. F. Clarke[5] gives the limits of the long diameter as 50 mm. and 90 mm., and the maximum and minimum short diameters as 45 mm. and 28 mm. No such extremes in size were noticed among the eight hundred or more eggs that were examined.

[5] _Journal of Morphology_, vol. v.

[Illustration: FIG. 9. AN ALLIGATOR’S NEST, SOMEWHAT SMALLER THAN THE ONE REPRESENTED IN FIG. 8, BUILT CHIEFLY OF FLAGS.

The nest has been opened to show the irregularly arranged mass of eggs inside. The size and shape of the egg are shown by the one in the guide’s hand. (From a Photograph by the Author.)]

_Economic Importance._[6] More than one hundred years ago attempts were made to utilize the skin of the alligator, but it was not until about 1855 that these attempts were successful and alligator leather became somewhat fashionable and some thousands of hides were converted into leather. The demand was short-lived, however, and was not again felt until the demand for shoe-leather during the war between the States revived the business. At the close of the war the business again failed, but about 1869 the demand became greater than ever and has continued unabated to the present time. The supply of skins from our own States proving inadequate, large numbers of skins were soon imported from Mexico and Central America. The skins from South America are so heavy that they are of little value in making leather. Of the States of the Union, Florida has been the chief producer, the most important centers for hides being Cocoa, Melbourne, Fort Pierce, Miami, and Kissimmee. Ten men at the first-named place took, in 1899-1900, 2500 skins; one man took 800 skins in one year; another man collected 42 skins in one night. At Fort Pierce twelve men took 4000 skins in 1889. In 1899, three firms at Kissimmee handled 33,600 hides. After this time the total number of hides taken and the average per man diminished greatly.

[6] The following figures are from an article by C. H. Stevenson in the Report of the Bureau of Fisheries, 1902, pp. 283-352.

Besides being killed for their hides, the alligators have been destroyed by the thousands merely for wanton sport, so that in 1902 it was estimated that their numbers in Florida and Louisiana were less than one fifth of what they were twenty years before that time, and unless steps be taken to prevent it, the alligator hide, as an article of commerce, may cease to exist in our Southern States.

It has been claimed that the destruction of the alligator has allowed the cane rat and muskrat to increase to a serious extent, the former doing great damage to crops, the latter often injuring the levees to a dangerous extent. Legislation to forbid the killing of alligators of less than five feet in length has been suggested and should be passed, since animals of less size have almost no commercial value for leather.

In 1902, the annual output from the tanneries of the United States approximated 280,000 skins, worth about $420,000. Of these about fifty-six per cent. came from Mexico and Central America, twenty-two per cent. from Florida, twenty per cent. from Louisiana, and the remaining two per cent. from the other Gulf States. South American hides are not handled by the United States markets.

In 1908, there were marketed from the South Atlantic and Gulf States 372,000 pounds of alligator hides, valued at $61,000.

According to the United States Bureau of Fisheries the hunter in 1891 averaged about 60 cents for the skin, while in 1902 the price averaged about 90 cents, varying between 15 cents and $2.00, depending on the size and condition of the skin. “Prime hides five feet long, with no cuts, scale slips, or other defects, are worth about 95 cents each, in trade, when the hunter sells them at the country stores, and about $1.10 cash, at the tanneries. Those measuring seven feet are worth $1.55, six feet, $1.12; four feet, 52 cents, and three feet, 25 cents. Little demand exists for those under three feet in length” (Report Commissioner of Fish and Fisheries, 1902, p. 345). Hides of seven feet are in most demand, those over ten feet are not much used. The income of the hunters is largely increased by the sale of otter, bear, deer, and other skins.

The different varieties of skins are described by Stevenson (74) as follows:

“There are several distinct varieties of alligator skins on the markets, the most important being the Floridian, Louisianian, and Mexican; each differs from the others in certain well-defined characteristics, and owing to these differences each variety has its special uses.

“The Florida skins are longer in the body--that is, from the fore legs to the hind legs--than those from Louisiana and Mexico, and consequently they are largely in demand by manufacturers of large handbags. They also have a number of so-called ‘buttons’ or ‘corn marks’ on the inside or under surface of an equal number of the scutes resulting from imbedded horn-like tissues in the center of those scales. These increase the difficulty in tanning the skins and detract somewhat from the appearance of the finished article, and for this reason the Florida skins are ordinarily the cheapest on the market. The farther south the skins are secured in Florida the greater the number of ‘corn marks,’ and those from the vicinity of Key West are almost valueless for this reason.

“The Louisiana skins differ from those of Florida in the absence of the ‘corn marks’ above noted, and from both the Florida and Mexican skins in being more pliable and in having the scales more artistically curved and shaped. Consequently they are preferred for such small articles as card-cases and pocketbooks, and usually sell at the highest prices. Skins obtained in Mississippi and Texas are similar to those secured in Louisiana, while those from Georgia and South Carolina are similar to those from Florida, except that the ‘corn markings’ are not so numerous. All the Florida and Louisiana skins show greater uniformity of coloring, being of a bluish black on the upper surface and a peculiar bluish white on the under side.

“In addition to an absence of the characteristics above noted the Mexican and Central American skins are distinguished by having from one to four small dots or markings like pin holes near the caudal end of each scale. The length of the Mexican skins varies greatly in proportion to the width, sometimes equaling that of the Florida skins. Those from the east coast of Mexico are the best, being lighter in color and with neat and attractively shaped scales. The west coast skins are yellowish in color when in the green state, and the scales are larger and not so artistically formed. The Florida and Louisiana skins are almost invariably split down the back, or rather along each side of the back, so as to preserve the under side in a solid piece, but most of the Mexican skins are split down the middle of the abdomen, keeping the back intact, making what is commonly known as ‘horn alligator.’ (See Fig. 15.)

“The skin should be removed soon after death as, in warm climates, putrefaction sets in very early and the value of the skin is depreciated. After removal, the flesh side of the skin is thoroughly rubbed with fine salt, and the skin is carefully rolled up with the salted side inside and is ready for shipment, but must be kept in a dry, cool place. Great care must be taken not to cut the hide since small cuts that are not noticeable in the raw skin may be so conspicuous in the dressed skin as to render it of much less value; a large percentage of the hides received in the markets are thus damaged.

“Formerly only the ‘belly skin’ was removed, by two longitudinal incisions just below the horny portion of the back; but it was later found that the thick horny skin of the back could be tanned nearly as well as the thinner belly skin, so that the entire skin is now usually removed by a longitudinal incision along the mid-ventral line, with lateral incisions along each leg to the foot (Fig. 15). The entire skin is more commonly taken in Mexico and Central America than in our States.

“Although the raw skins are sold according to length, the tanned hides are sold by the width of the leather at the widest part. Standard hides sell for $1.00 to $1.65 per twelve inches of width. Some skins tanned and dyed in a superior manner sell for $2.00 or more for single skins of 2¹⁄₂ feet in length. As a rule the Louisiana skins fetch the highest prices, and those from Florida the lowest. Imitation alligator leather is now prepared in large quantities, principally from sheepskins or the buffing from cowhides. These are tanned according to the usual process, and before the skins are finished they are embossed with the characteristic alligator markings by passing them between two rollers.” (Above-mentioned report, p. 346.)

Very little of the leather is now used in making shoes, the chief demand being for handbags, music-rolls, etc.

In hunting alligators for their hides two methods are usually employed, in our Southern States at least. The common method is “fire-hunting” at night; the hunters here go, either singly or in pairs, usually in boats, sometimes on foot, with shotgun and torch. The torch may be fastened to the hunter’s hat, after the manner of the miner’s lamp. One more progressive hunter that I knew had, as a torch, an acetylene lamp, attached to his hat, with the tube for the gas extending down his back to the generator in his pocket. This lamp threw a blinding beam of light far across the swamp into the eyes of the unsuspecting ’gator, which usually remained fascinated until it could be approached to within easy range. A shotgun at close range, of course, blows off nearly the entire top of the animal’s head and kills it instantly; it is then seized before it sinks out of reach and is either taken into the boat or dragged upon the bank to be collected with others in the early morning.

In daylight, with no glaring light to hypnotize it, the alligator is difficult to approach within range and it usually disappears into its cave before the hunter can get a shot at it. The daylight hunter, then, should be supplied not, of course, with a light, but with a ten- or fifteen-foot pole with a large iron hook at the end. If the alligator be vigorously prodded with this mammoth fishhook he will usually finally seize it with his mouth and can be pulled out of his hole alive. It is then an easy matter to kill him with a bullet through the base of the brain. I have seen an eight-foot alligator thus killed with a little .22 calibre “cat” rifle. An eight-foot alligator will often be all that two men can manage to drag out of his cave in this way; and, in the torrid heat of the Southern swamp, this violent exercise is not to the liking of the usually not very energetic hunter.

While the manufacture of leather gives the chief value to the alligator there are other ways in which it has some economic importance. Chief of these is probably the sale of alligator goods to tourists. In 1891 there were in Jacksonville, Florida, twelve dealers in live and stuffed alligators. In 1890, 8400 alligators were sold to tourists, the price for the live animals varying from $10.00 to $35 per hundred. For individual animals of the smallest size (less than twelve inches long) the price is usually from 50 cents to $1.00. For a three-foot alligator the price is generally $3-$5.00; for sizes over three feet $2.00 per foot may be charged, though for very large specimens the price may be from $50 to $300 each.

Besides the live and stuffed animals the teeth are polished and sold as souvenirs; about 450 pounds of teeth were sold in 1890, at a price varying from $1.00 to $2.00 per pound. From 75 to 200 teeth will make a pound.

In 1891 about forty people, in addition to the regular dealers, were engaged, in the United States, in stuffing alligators, polishing teeth, etc. The teeth are extracted by burying the head until decomposition sets in.

The tiny alligators that are most commonly sold to tourists, to be brought North, perhaps, and allowed to freeze or starve to death, may either be caught by a wire noose at the end of a fishing rod, or they may be hatched from eggs that are taken from the nests shortly before they are ready to hatch. Such eggs may readily be hatched by simply keeping them moist and at a fairly constant temperature, as has been previously noted. Besides the above uses Ditmars says: “The eggs are eaten in many portions of the South, and the search for eggs at the proper season furnishes profitable employment for many persons, as each nest contains a large number of eggs.”

[Illustration: BROAD-NOSED CAIMAN. (_Caiman latirostris._)

Distribution: Tropical South America.

Attains a length of about seven feet. (After Ditmars.)

(Reproduced by Permission of Sturgis & Walton Co.)]

[Illustration: FIG. 10. SPECTACLED CAIMAN. (_Caiman sclerops._) Tropical America.

The length of an adult is about eight feet. (After Ditmars.)

(Reproduced by Permission of Sturgis & Walton Co.)]

Never having eaten an alligator egg I cannot speak from personal experience of its flavor; but it has always seemed strange to me that more use is not made of the flesh of the alligator. This flesh is often said to have too strong a flavor to be palatable; I have eaten it when it had no such rank taste but was decidedly agreeable, being, as might perhaps be expected of so amphibious an animal, somewhat like both fish and flesh, yet not exactly like either. Perhaps greater care should be taken in skinning an animal that is to be used for food in order that the flesh be not tainted with the musk. It may be a lack of care in preparation that has given rise to the impression that alligator meat is too strong to be pleasant. It is perhaps, also, the “idea” of eating a reptile that makes the meat unpopular. A half-grown boy, who was once in the swamps with me, had expressed a great aversion to alligator meat, so the guide, one day, offered him a nicely fried piece of alligator meat, saying it was fish; the meat was eaten with evident relish and the diner was not told until after a second piece had disappeared what he had been eating. It always seemed strange to me that the poor people of the South should not more often vary the monotony of fat pork and corn bread with alligator steaks. Whether the meat could be smoked or salted so that it would keep in a hot climate I do not know; I am not aware of any experiments along this line.

The Chinese Alligator

Beside the American form, _Alligator mississippiensis_, the only other species of alligator is found in China, along the Yang-tse-Kiang River; it is _Alligator sinensis_. It reaches a length of six feet and externally resembles its American relative; it is greenish black above speckled with yellow; grayish below.

The Caiman

This is the nearest relative of the alligator and is found in Central America and tropical South America. As seen by the table on page 2, it is usually a small animal, though one species, the black caiman, is said to reach a length of twenty feet (Fig. 10). The nasal bones do not form a bony septum as in the alligator and the ventral armor consists of overlapping bony scutes. The canine teeth of the lower jaw fit into a pit in the upper jaw, as in the alligator.

They are said by some writers to be extremely abundant in the waters of the upper Amazon, migrating to the flooded forests during the rainy season and returning to the streams on the approach of the dry season. According to Ditmars there are five species of caiman of which the spectacled caiman, _C. sclerops_, and the black caiman, _C. niger_, are the most striking. The former is so named because of the spectacled appearance due to the swollen and wrinkled upper eyelids; it reaches a length of eight feet and is said to be of a treacherous disposition. The latter has a blunt snout like the alligator and is the largest of the New World crocodilians.

The American Crocodile

Of about a dozen existing species of crocodile, but one, the American crocodile, _C. americanus_, is found in the United States, and it is limited to the swamps and coast of southern Florida below Lake Worth; its greater sensitiveness to cold is doubtless the cause of its not being found so far north as the alligator. Its range extends south through Mexico and Central America into South America. It was first found in Florida by Dr. Hornaday in 1875. It sometimes reaches a length of fourteen feet.

As has already been noted there is, besides certain structural differences, a marked difference in the dispositions of the Florida alligator and crocodile. While an alligator may snap its jaws, hiss, and swing its tail from side to side, it is not difficult for a couple of men with ropes and a pole to safely tie up a large specimen. The struggles of a crocodile are of a more serious nature. Ditmars thus describes an encounter with a captive Florida crocodile: “The writer well remembers his first acquaintance with a big fellow from Florida. Driven out of the crate the crocodile looked the picture of good nature. Standing away from what he thought to be the reach of his tail, the writer prodded the apparently sluggish brute with a stick to start it for the tank. Several things happened in quick order. With a crescentic twist of the body utterly beyond the power of an alligator, the brute dashed its tail at the writer, landing him such a powerful blow that he was lifted completely from the ground. As he left _terra firma_, an almost involuntary inclination caused him to hurl his body away from a pair of widely-gaping, tooth-studded jaws swinging perilously near. Landing with a thud on one shoulder, though otherwise unhurt, the writer threw himself over and over, rolling from the dangerous brute that was actually pursuing him on the run, body raised high from the ground. For an instant it seemed as if the crocodile would win. As the writer sprang to his feet and glanced backward, he beheld the brute throw itself flat on its belly, open the jaws widely, then remain motionless as a statue. Such is the average crocodile--an active, vicious and, above all, treacherous brute.” Ditmars says again, in the same book: “When the keepers of the reptile house of the New York Zoölogical Park clean out the big pool of the crocodilians, they actually walk over the backs of some of the big ’gators, so tame are these. They never become unduly familiar with the crocodiles, finding it necessary to pen the latter behind heavily barred gates--and in the process the men are often chased from the enclosure.”

[Illustration: NILE CROCODILE. (_Crocodilus niloticus._)

Distribution: Africa generally; Madagascar.

Grows to a length of sixteen feet. (After Ditmars.)

(Reproduced by Permission of Sturgis & Walton Co.)]

[Illustration: FIG. 11. WEST AFRICAN CROCODILE. (_Crocodilus cataphractus._)

Distribution: West Africa.

Does not attain so large a size as the Nile Crocodile. (After Ditmars.)

(Reproduced by Permission of Sturgis & Walton Co.)]

In contrast to this ferocious aggressiveness in captivity the American crocodile is said to be very timid and retiring when in its native habitat.

Young animals are greenish with black marking; as they become older they are of an olive color, and old specimens are dull gray.

THE ORINOCO CROCODILE, _C. intermedius_

This is a species with a very narrow snout that is not quite so large as the preceding. It is said to be abundant in the Orinoco River and its tributaries.

Besides the two above mentioned there is a small species, _C. rhombifera_, found only in Cuba and hence known as the Cuban crocodile.

THE AFRICAN OR NILE CROCODILE, _C. niloticus_

This well known and much feared species is found throughout the continent of Africa, and is very common on the island of Madagascar (Fig. 11). In the lower waters of the Nile it is now nearly exterminated. It has always been a conspicuous animal in Egypt and was one of the animals held sacred by the Egyptians and preserved by them as mummies. It is discussed by Herodotus, and the “leviathan” mentioned in the Book of Job is doubtless this crocodile. In fact the name is said to be derived from the ancient Greek for lizard, just as the word alligator is said to be derived from the Spanish for lizard--_el lagarto_; the resemblance in form between these big saurians and their smaller relatives is evident. The alligator, being confined to America and a small part of Asia, was probably not known to the ancients.

An excellent account of the development and habits of the present species is given by Voeltzkow (78), who says it is, perhaps, the most common vertebrate in Madagascar. The largest specimen measured by this observer was thirteen feet; Ditmars gives sixteen feet as the maximum size. This _man-eating_ crocodile, according to Ditmars, destroys more human lives than any other wild animal of the dark continent.

The story told by Herodotus of the bird, probably a species of plover, which enters the gaping mouth of the crocodile to pick off the leeches found there may be true, since there is such a bird that may be seen perching on the backs of crocodiles, and as the Crocodilia frequently lie with their mouths wide open it is quite possible that these birds may pick off the worms that are often found within. It is also possible that the alertness of these birds to danger may serve as a warning to the crocodiles with which they associate.

[Illustration: FIG. 12. SALT-WATER CROCODILE. (_Crocodilus porosus._)

Distribution: India to North Australia. Occurs at sea.

Grows to a length of twenty feet. (After Ditmars.)

(Reproduced by Permission of Sturgis & Walton Co.)]

According to Voeltzkow these crocodiles dig caves of thirty-nine to forty feet length in the banks of the streams they inhabit, into which they retire on the approach of danger. The caves open under water and slope upward towards the surface of the ground where a few small air-holes are found. The natives locate the caves by means of the air-holes and dig out the hidden animal, first stopping up the entrance.

In Madagascar the eggs are laid in August and September and hatch in about twelve weeks; they are laid at night, usually shortly before daybreak. From twenty to thirty eggs are laid in one nest, which is merely a hole dug in the dry sand. As was said in connection with the Florida alligator, the habits of the two animals are quite different in this respect,--the moisture that is so important in the one case is fatal to the embryo in the other. When the eggs are laid the nest is filled in with sand so that there is nothing to indicate its position except that the female crocodile is in the habit of lying on the spot where her eggs lie buried.

Like the alligator the young crocodile makes a squeaking noise shortly before hatching and the mother doubtless opens the nest, at this time, to allow the young to escape. A fence that Voeltzkow built around a nest was repeatedly broken down by the mother in attempting to get back to her eggs.

The character of the crocodile’s egg is discussed, in comparison with that of the Florida alligator, on page 23.

THE MARSH CROCODILE OR MUGGER, _C. palustris_

Found in India, Ceylon, Burmah, the Malay Peninsula, and many of the islands in that region. It has a rather broad snout, and reaches a length of twelve feet. It is a timid form and is harmless to man. It is frequently venerated by the Hindoos and is kept in a semi-domesticated condition in ponds where it is fed and becomes very tame.

In the dry season when the natural ponds are empty they sometimes migrate overland in search of water, but generally they bury themselves in the mud and lie dormant until the rains begin again.

THE SALT-WATER CROCODILE, _C. porosus_

This is one of the largest if not the largest of living reptiles (Fig. 12). It is said by Ditmars to reach a length of twenty feet and there is a record of one specimen that was thirty-three feet in length. It is said to be easily recognized by the prominent, longitudinal ridge that extends in front of each eye, over the prefrontal bone, and by the absence of the suboccipital scutes.

[Illustration: FIG. 13. SKULL OF GAVIAL.

(Dorsal View.)

(Photograph from U. S. National Museum.)]

[Illustration: FIG. 14. SKULL OF GAVIAL.

(Lateral View.)

(Photograph from U. S. National Museum.)]

It is typically an inhabitant of tidal waters and is sometimes found swimming at sea, out of sight of land; it seldom goes inland to any great distance from the sea. It is a _man-eating_ species and many human lives are said to be destroyed by it in India and surrounding countries. A British “blue book” states that in British India 244 deaths were caused by Crocodilia in the year 1910.

In captivity it is savage and untamable. Ditmars, in speaking of three specimens that he had in captivity, says they were “positively the most vicious reptiles” he had ever seen.

THE INDIAN GAVIAL, _Gavialis gangeticus_

This animal, which inhabits the Ganges and other rivers of northern India, is, with the possible exception of the preceding species, the largest of the Crocodilia; it is said to reach a length of thirty feet, which is twice that of a very large Florida alligator. As previously noted its snout is extremely long and narrow (Figs. 13 and 14), with a large, fleshy hump at the tip, that projects above the muddy water in which the animal lies concealed.

It is a timid animal and, in spite of its huge size, dashes quickly into the water on the approach of man, to whom it is seldom or never dangerous. Its Indian name, _gharial_, from which its generic name has been corrupted, means fish-eater, since its food consists, it is said, largely if not entirely of fish.

Considering its huge size and the character of its jaws and teeth as shown in Figures 13 and 14, it is fortunate that it prefers fish to human flesh.

Anderson (2) describes the eggs and young of the Indian gavial. He found forty eggs in a nest of sand; they were in two layers, with a foot of sand between them. The young were 15.8 inches long at hatching. He says: “The young run with amazing rapidity the moment they are out of the shell.... Some of them actually bit my fingers before I had time to remove the shell from their bodies.” The following quotation from Oldenburg (46), for which I am indebted to Dr. Hussakof, is perhaps the earliest reference to the egg of the American alligator. It also mentions the habit that is practiced by some of the recent Crocodilia of swallowing stones to aid in digestion, as was apparently done by some of the large extinct reptiles.

“The eggs of _Crocodiles_ and _Alligators_ are little bigger than a Turkey’s. I thought to bring one to England, but it was lost. I never broke any to see the Yolk and White; but the Shell is as firme and like in shape to a Turkey’s, but not spotted. I inquired into the Stone in the Stomach of a _Cayman_ or _Crocodile_, and I found by the inquiry of a very observing gentleman there, that they were nothing but several Stones, which that Creature swallows for digestion. He took out of one a piece of a Rock as big as his head: out of others he had taken sixteen or twenty lesser. None regards them much there, whatever _Monardes_ relateth.”

Chapter II

The Skeleton

A. The Exoskeleton

The exoskeleton is well developed in the Crocodilia, and forms a very considerable protection to its bearer. It is both dermal and epidermal in origin.

The _epidermal skeleton_ of the alligator consists of oblong horny scales, arranged in transverse rows; the long axes of the scales are parallel to that of the body. On the tail, except along the mid-dorsal line, and on the ventral side of the trunk and head these scales are very regular in outline and arrangement; on the sides of the head and trunk and on the legs they are much smaller and less regularly arranged, while along the mid-dorsal line of the tail, especially in its posterior half, they are elevated into tall keels that give the tail a large surface for swimming. The first three digits of both manus and pes are armed with horny claws, which also belong to the epidermal part of the exoskeleton.

[Illustration: FIG. 15. ALLIGATOR SKINS; UNDER-SURFACE AND HORN-BACK.]

The _dermal exoskeleton_ consists of bony scutes that underlie the epidermal scales of the dorsal surface of the trunk and anterior part of the tail. The overlying scales, except in very young animals, are always rubbed off, so that the bony scales are exposed. The ventral or inner surface of the scutes is flat, while the outer surface is strongly keeled and in old animals is often rough and pitted. The plates are nearly square in outline and are closely joined together in most places.

The scutes are grouped in two fairly distinct areas known as the nuchal and the dorsal shields. The former lies just back of the head, in the region of the fore legs, and consists of four larger and a number of smaller plates (Fig. 15). The latter, or dorsal shield, extends over the back in fairly regular longitudinal rows and quite regular transverse rows. At the widest part of the trunk there are six or eight of these scutes in one transverse row. They become smaller towards the tail.

The _teeth_ are exoskeletal structures, partly of ectodermal, partly of dermal origin. They are conical in shape, without roots, and are replaced when lost. They will be described in connection with the skull.

Musk glands, said by Gadow to be present in all Crocodilia, are found in both sexes and are derivations of the skin. One pair, each of which may be as large as a walnut, is found on the lower side of the head, one on the inside of each half of the mandible. The other pair is inside of the lips of the cloaca.

_The Histology of the Integument._ To understand the structure of the integument of the Crocodilia it is well to begin with the embryo. A cross section of the epidermis of such an embryo will show the rete Malpighii as a single layer of short, cylindrical cells; over these are found more or less flattened, disk-shaped cells formed by transverse division of the underlying cells of the rete. On the outside lies the epitrichial layer which consists of a mosaic of polygonal cells, near the middle of each of which lies an oval nucleus. Between the epitrichial cells are small oval holes, not unlike the stomata in the epidermis of plant tissues. Bronn thinks these are not artifacts, but he does not suggest any explanation of their occurrence.

In the epidermis of young and half-grown animals the rete Malpighii is seen still as above noted. On these cylindrical cells are found flattened cells that gradually become very flat and lose their nuclei as they pass over into the horny layer.

The stratum corneum consists of strongly flattened cells in which the nuclei can no longer be clearly seen, though their location can usually be determined by the groups of pigment granules. On the cells of the more superficial layers of the stratum corneum are seen straight, dark lines, perhaps ridges caused by pressure of the over- or underlying polygonal cells. The individual cells of the horny layer are usually easily isolated in the belly and neck regions where they never become very thick; but in the back the cells in this layer are very numerous and fuse with each other to form the bony plates; here the rete is the only clearly differentiated layer. Whether prickle cells are present in the epidermis of the crocodile Bronn is not certain, though he thinks they probably are.

Rathke pointed out that on the surface of certain folds of the integument, especially in the region of the jaws, are found in all Crocodilia certain small, scattered, wart-like elevations, around each of which is customarily a narrow, shallow, circular groove; they usually have a dark brown but sometimes a gray or even white color. Microscopic examination shows these warts to be of epidermal origin, consisting of bright, round cells that are closely united, without visible intercellular substance. Treatment with potassium hydroxid and then with water will show sometimes, though not always, fine granular nuclei in the cells.

In probably all members of the genus Crocodilus at least is found, on the thick swelling on the right and on the left side of the neck and trunk, a small, flat pit which has the appearance of the opening of an integumental gland. The pits are present also in the scales of the throat, under the side of the neck, sides of the body, lateral and ventral surfaces of the anterior half of the tail, and the legs. They are near the hinder border of the scales. Only occasionally are two pits found in one scale. These pits are found in the gavials but are absent in some, probably all, alligators. A small knob projects from the center of some of the pits. These pits are not openings of glands but have about the same structure as the pits seen in the head.

The integumental bones in the Crocodilia originate in the connective tissue of the cutis. Investigations in young animals show that these bones usually take their origin in the under and middle layers of the cutis and generally work towards the periphery.

B. The Endoskeleton

_I. The Vertebral Column._

[Illustration:

FIG. 16.--Skeleton of Crocodile. _D_, dorsal region; _L_, lumbar region; _Sa_, sacral region; _Ri_, ribs; _Sc_, scapula; _H_, humerus: _R_, radius; _U_, ulna; _Sta_, sternum abdominale: _Fe_, femur; _T_, tibia; _J_, ischium; _C_, caudal vertebræ. (From Claus & Sedgwick.)]

The vertebral column consists of about sixty-five vertebræ, which may be separated into the usual regions; there are nine cervical, ten dorsal, five lumbar, two sacral, and about thirty-nine caudal. It is likely that the number of caudals may be subject to frequent variation; one complete skeleton had sixty-five vertebræ in all, another had sixty-eight. A complete skeleton of the crocodile (species not known) had sixty vertebræ. A thirteen-foot skeleton at Western Reserve University had only sixty-one vertebræ, but some of the caudals were evidently missing. Two skeletons of _C. porosus_ in the museum at Singapore had sixty and sixty-three vertebræ respectively. A skeleton of _Tomistoma schlegeli_ in the same museum had sixty vertebræ.

_The Cervical Vertebræ._ Since all of the cervical vertebræ bear ribs, we shall assume the distinction between them and the dorsal vertebræ to be that the ribs of the latter meet the sternum, while those of the former do not reach to the sternum. Assuming this distinction, there are, as was said above, nine cervical vertebræ.

[Illustration: FIG. 17. FIRST FOUR CERVICAL VERTEBRÆ OF A CROCODILE

(_C. vulgaris_). (From Reynolds, partly after Von Zittel.)

1. pro-atlas. 2. lateral portion of atlas. 3. odontoid process. 4. ventral portion of atlas. 5. neural spine of axis. 6. postzygapophysis of fourth vertebra. 7. tubercular portion of fourth cervical rib. 8. first cervical rib. 9. second cervical rib. 10. convex posterior surface of centrum of fourth vertebra.]

With the exception of the first two, to be discussed later, these are all essentially alike and the fourth will be described as a type (Fig. 17). Its centrum is cylindrical or somewhat hourglass shaped, concave anteriorly and convex posteriorly; it is not completely fused with the neural arch but is united with it by sutures. From the anterior end of the ventral surface of the centrum projects downward and forward a small plow-shaped process, the hypapophysis. On each side of the centrum, near its anterior end, is a facet with which the lower branch (capitulum) of the rib articulates. The neural arch is strongly developed and is extended dorsally into a prominent neural spine and on each side as a short, blunt, transverse process with which the tubercle or upper branch of the rib articulates. Posteriorly the arch is notched on each side to form the openings for the exit of the spinal nerves. Projecting dorsally and anteriorly from the arch are two short processes which bear the medially and dorsally facing prezygapophyses (Fig. 17). Just caudad to these processes are somewhat shorter processes that bear the laterally and ventrally facing postzygapophyses (Fig. 17, 6).

The _atlas_, as in other vertebrates, is highly specialized. It consists (Fig. 17), even in the adult animal, six feet or more in length, of four distinct portions, a ventral (4), a dorsal (1), and two lateral (2) parts. The ventral portion is relatively more massive than in most animals; its anterior surface is concave and forms the main part of the articular surface for the occipital condyle of the skull. Its postero-dorsal surface articulates with the odontoid process of the axis. On its postero-lateral surfaces are the facets for articulation with the first ribs, which, unlike the other cervical ribs, have but one articular surface. Articulating dorsally with this ventral element of the atlas are the two rather heavy lateral elements which form the neural arch. Anteriorly they form the lateral parts of the articular surface for the condyle and dorsally they unite for a short distance with each other. Projecting ventrally from the posterior part of their dorsal portion are the small postzygapophyses. Ventrally and laterally they articulate with the odontoid process (Fig. 17, 3). Projecting dorsad and cephalad from the dorsal surface of these lateral elements is the dorsal element of the atlas (Fig. 17, 1), the pro-atlas, which may not be properly a part of the vertebral column at all, since it is said to be merely a membrane bone. Gadow says it is the detached neural spine of the atlas. It is thin and triangular in shape, resembling in contour a large, mammalian epiglottis. It forms an arch over the space between the skull and the front of the atlas proper. Reynolds calls it the pro-atlas.

_The Axis._ The centrum differs from those following it (described above) mainly in its close articulation (not fusion) with the large odontoid process; this process not only projects into the atlas, as is usually the case, but articulates with its postero-lateral border on each side, and is distinctly visible in a lateral view of the neck (Fig. 17, 3). Like the rest of the cervical vertebræ the posterior surface of the centrum is convex. The neural arch of the atlas differs from those following mainly in having a much wider (in an antero-posterior direction) neural spine. The lateral processes and those bearing the prezygapophyses are also less strongly developed than on the following vertebræ.

[Illustration: FIG. 18. ANTERIOR VIEW OF A, A LATE THORACIC AND B, THE FIRST SACRAL VERTEBRA OF A YOUNG CROCODILE

(_C. palustris_). × ¹⁄₃. (After Reynolds.)

1. neural spine. 2. process bearing prezygapophysis. 3. facet for articulation with the capitulum of the rib. 4. sacral rib. 5. surface which is united with the ilium. 6. concave anterior face of centrum.]

_The Thoracic Vertebræ._ The first thoracic vertebra differs scarcely at all from the ninth cervical; and the tenth thoracic differs from the first lumbar only in bearing a short rib. Only the first three thoracic centra bear the hypapophyses noted in connection with the cervical vertebræ. The ribs of the first two thoracic vertebræ articulate with them by two processes, as in the typical cervical vertebræ; the other ribs articulate only with the transverse process. The fourth thoracic may be described as a type of this region (Fig. 18, A). Its centrum is rather longer than in the first two thoracic and in the cervical vertebræ and has no process for articulation with the head of the rib, otherwise it is essentially the same. Like all of the vertebræ behind it and unlike those in front it is apparently completely fused with its neural arch. The neural arch is very broad (in an antero-posterior direction) and is extended dorsally as a wide neural spine (1). The neural spines of the following thoracic and the first two or three lumbar vertebræ are increasingly broad and truncated. The transverse processes are very broad, long and thin, and in the third to eighth vertebræ they have two articular surfaces, an anterior and more medial one for articulation with the head of the rib (3) and a posterior and more distal one for articulation with the tubercle of the rib. These two surfaces approach each other as the vertebræ are followed caudad until, in the last two thoracic vertebræ, they form practically one surface. The processes of the pre- and postzygapophyses spring from the arch at the base of the transverse process; the former surface is directed dorsally and medially, the latter ventrally and laterally. The intervertebral foramina are smaller and more nearly circular than in the cervical region, and are more closely surrounded by bone.

_The Lumbar Vertebræ._ The five lumbar vertebræ are essentially like the thoracic except that the transverse processes, which, of course, bear no ribs, are both shorter and narrower. The postero-lateral border of the centrum of the last of these five vertebræ has a small surface for articulation with the antero-medial border of the transverse process of the first sacral vertebra.

_The Sacral Vertebræ_ (Fig. 18, B). These are two in number. The centrum of the first is concave in front and flat behind, instead of being convex behind, and the second is flat (instead of concave) in front, and convex behind. The neural spine and zygapophyses are as in the lumbar region. Projecting laterally from each sacral vertebra, forming a close, sutural joint with both centrum and neural arch, is a heavy bone shaped like a truncated pyramid (4); the base of the pyramid is ankylosed with the ilium. These bones seem to be much thickened transverse processes, but since they are not completely fused with their respective vertebræ and are said to ossify separately they should probably be called sacral ribs. The two sacral vertebræ do not seem to be any more closely united than are any other two vertebræ.

_The Caudal Vertebræ_ (Fig. 16, _C_). These are characterized by the entire absence of ribs, and by the presence on all but the first and the last four or five of V-shaped chevron bones. The first ten or twelve of these chevron bones articulate chiefly with the postero-ventral ends of the centra, but they also articulate with the antero-ventral ends of the vertebra behind themselves; and as they are followed caudad they seem to lie directly below the intervertebral regions and to articulate equally with the vertebræ before and behind. The chevron bones gradually diminish in size from before back. The neural processes of the first four or five caudals are broad, like those of the more anterior regions, but caudad to this point they become narrower and more pointed, though they retain the same height until about the last ten or twelve vertebræ. Towards the tip of the tail the dorsal spines diminish in height and finally disappear. The transverse processes of the first five or six of the caudals are long and narrow. They gradually diminish in length until the eighteenth caudal, back of which they are no longer to be seen. The zygapophyses are mostly about the same as in the more anterior vertebræ, but towards the posterior end of the tail the postzygapophyses come to lie between rather than above the prezygapophyses. The neural canal diminishes, of course, in size towards the tip of the tail until it is no longer present, the last five or six vertebræ consisting only of the centra.

_II. The Skull._

The skull of the alligator is very massive and has several peculiarities. 1. The bones of the dorsal surface are rough and pitted, especially in old animals. 2. The jaws are enormously large in proportion to the brain cavity, and are armed with many large teeth. 3. The mandibular articulation is some distance caudad to the occipital condyle. 4. The interorbital septum is mainly cartilaginous. 5. There is a complicated system of Eustachian passages connecting with the back of the mouth by a single opening. 6. The posterior nares are placed very far back and the palate is correspondingly long.

The skull as a whole may be divided into three regions: the cranium, the lower jaw, and the hyoid; these will be described in the order given.

_The Cranium._ As a matter of convenience the bones will be described as seen from the different aspects--dorsal, ventral, lateral, posterior, and in sagittal section--without particular regard to their grouping into segments or regions.

_The Dorsal Aspect_ (Fig. 19). At the extreme posterior end of the median line lies the _parietal_ (23), double in the embryo but a single bone in the adult. It forms a part of the roof of the cranial cavity and articulates anteriorly with the frontal, laterally with the postfrontals, squamosals, and, according to Reynolds, with alisphenoids, pro-otics and epiotics, and ventrally with the supraoccipital. It forms the median boundary of each of the two _supratemporal fossæ_ (sf).

On each side of the parietal and forming the posterior comers of the rectangular postero-dorsal region of the skull are the _squamosals_ (7). Each squamosal articulates medially with the parietal, anteriorly with the postfrontal, and ventrally with the quadrate and exoccipital. It forms part of the posterior and lateral boundaries of the supratemporal fossa and a part of the roof of the external auditory meatus.

Articulating with the anterior border of the squamosals and forming the anterior corners of the rectangular region mentioned above are the _postfrontals_ (6). The postfrontal articulates medially with the parietal and frontal, and ventrally with the alisphenoid and a small part of the quadrate. It sends, in a ventro-lateral direction, a thick process that unites with a similar process from the jugal to form the _postorbital bar_ (pb) which lies between the orbit (o) and the temporal fossa (tf). The postfrontal forms the antero-lateral boundary of the supratemporal fossa.

Articulating posteriorly and laterally with the parietal and the postfrontals, and forming the highest point of the skull, is the single _frontal_ bone (24), which, like the parietal, is paired in the embryo. It is a heavy bone whose dorsal surface is flattened posteriorly, deeply concave in the middle region, and drawn out into a long projection anteriorly. It forms part of the roof of the cranial cavity and articulates ventro-laterally with the alisphenoid and anteriorly with the prefrontals and nasals. It forms a part of the median boundary of the orbit.

The _prefrontal_ (4) is an elongated bone in the latero-median border of the orbit. Medially and anteriorly it articulates with the frontal and nasal, laterally with the maxillary and lachrymal, and ventrally, by a heavy process, with the pterygoid.

[Illustration: FIG. 19. DORSAL VIEW OF THE SKULL OF THE ALLIGATOR (_A. Mississippiensis_).

1. premaxilla. 2. maxilla. 3. lachrymal. 4. prefrontal. 5. jugal. 6. postfrontal. 7. squamosal. 8. quadrate. 12. quadratojugal. 23. parietal. 24. frontal. 25. nasal. _an_, anterior nares; _o_, orbit; _pb_, postorbital bar; _sf_, supratemporal fossa; _tf_, lateral temporal fossa.]

The _nasal_ (25) is a long narrow bone forming the greater part of the roof of the nasal passage. Along the median line of the skull it articulates with its fellow; posteriorly with the frontal; laterally with the prefrontal and maxillary; and anteriorly with the premaxilla. In the crocodile, caiman, and gavial it also articulates with the lachrymal. In the alligator the anterior ends of the two nasals form a narrow rod of bone that extends across the anterior nares, and, meeting a projection from the premaxillaries, divides the opening into right and left halves. In the crocodile the nasals project only a very little way into the nares; in the caiman (according to Reynolds) they do not extend into the nares at all, and in the gavial, whose much elongated snout is mainly due to the great length of the maxillaries, the nasals do not extend more than a third of the distance from the prefrontals to the anterior nares.

The _maxilla_ (2) is a large bone that forms a large part of the upper jaw and that holds most of the teeth of that jaw. On the ventral side, as will be described later, it articulates with its fellow in the middle line, with the premaxilla, with the palatine, and with the transpalatine. Dorsally it articulates with the premaxilla in front; with the nasal and prefrontal on the medial side; and with the lachrymal and jugal behind.

The _premaxilla_ (1) forms, with its fellow, the extreme tip of the upper jaw. Each bone forms the anterior and lateral borders of its half of the anterior nares. It articulates medially with its fellow and posteriorly with the nasal and maxilla. Ventrally, as will be noted later, it bears five teeth and articulates with its fellow medially and with the maxilla posteriorly. Between the premaxillæ on the ventral side is the large anterior palatine foramen.

The _lachrymal_ (3) is a fairly large bone that forms the anterior border of the orbit. It is bounded laterally by the jugal, anteriorly by the maxilla, and medially by the prefrontals. Its postero-medial border is pierced by a large lachrymal foramen that extends lengthwise through the bone and opens, at its anterior end, into the nasal chamber.

The _supraorbital_, missing in the skull figured, is a small bone lying in the eyelid close to the junction of the frontal and prefrontal. Being unattached it is usually absent from prepared skulls.

The _jugal_ or _malar_ (5) is an elongated bone that forms a part of the lateral border of the head, on the one hand, and most of the lateral border of the orbit on the other. Anteriorly it articulates with the maxilla; medially with the lachrymal and prefrontal; posteriorly with the quadratojugal, and ventrally with the transpalatine. With the transpalatine it sends, in a dorso-medial direction, a process that meets the process, described above in connection with the postfrontal, to form the postorbital bar.

The _quadratojugal_ (12) is a small bone, wedged in between the jugal in front and the quadrate behind.

[Illustration: FIG. 20. VENTRAL VIEW OF THE SKULL OF THE ALLIGATOR (_A. Mississippiensis_).

2. maxilla. 5. jugal. 8. quadrate. 9. palatine. 10. pterygoid. 11. transpalatine. 12. quadratojugal. 14. basioccipital. _a_, anterior palatine vacuity; _eu_, opening of the median Eustachian canal; _pn_, posterior nares; _pv_, posterior palatine vacuity.]

The _quadrate_ (8) is more irregular and has more complicated articulations than almost any bone in the skull. Its posterior end, which forms the articular surface for the lower jaw, is elongated laterally and slightly concave. Anteriorly the quadrate articulates with the quadratojugal; medially with the basisphenoid and exoccipital; dorsally with the exoccipital, squamosal, postfrontal, and, possibly, with the pro-otic; ventrally with the pterygoid, alisphenoid, and probably with some of the otic bones. Its dorsal side forms most of the floor of the external auditory meatus which will be described later. While the basioccipital may be seen from the dorsal side, it is not really one of the dorsal bones of the skull and will be described later; the same is true of the pterygoids and palatines which may be seen through the empty orbits.

_The Ventral Aspect_ (Fig. 20). The larger part of this side of the skull is made up of four pairs of bones: the premaxillæ, the maxillæ, the palatines, and the pterygoids, lying, from anterior to posterior, in the order named.

The _premaxilla_ (1), as described in the dorsal view of the skull, is a triangular bone which, with its fellow, forms the anterior end of the snout. Each premaxilla bears five teeth, not only in the alligator but in the crocodile, the caiman, and in the gavial. Of these teeth the fourth from the front is the largest; the first two are small, and the third and fifth are of intermediate size. This arrangement as to size is also true, apparently, in the other groups of Crocodilia. The ventral surface of the premaxilla, which is more or less flat and horizontal, is pierced by a number of small foramina, in a row parallel to the curved outer margin of the bone. Between these foramina and the base of the teeth are four rounded depressions to receive the points of the first four teeth in the lower jaw; of these depressions the first and fourth are the deepest. The first pit often becomes so deep as to perforate the bone; this is true also with the crocodile and, according to Reynolds, with the caiman, but is not true of the gavial, whose interlocking teeth project outside of the jaws. It will be remembered that one of the chief distinctions, given early in this work, between the crocodile and the alligator is that in the former the fourth tooth in the lower jaw fits into a notch and not into a pit in the upper jaw.

The _maxilla_ (2), which with its fellow forms most of the hard palate, has also been mentioned in connection with the dorsal aspect. Each maxilla is notched, posteriorly, to form the anterior border of the posterior palatine vacuity, and together they are notched to receive the rectangular anterior ends of the palatines. The postero-lateral extremity of the maxilla articulates with the transpalatine. Along the outer border of the bone are the teeth, of which there are fifteen or sixteen in the alligator, about the same number (perhaps one or two less) in the caiman and crocodile, and about twenty-four in the gavial. The first or anterior eight or ten teeth have individual sockets, the rest are placed in a groove. In the crocodile none of the teeth have individual sockets, and in the gavial they all have sockets. The premaxillary and more anterior of the maxillary teeth are slightly recurved and are sharper than the posterior maxillaries which besides being blunt have a constriction above the surface of the socket.

The crocodilian tooth consists of three layers (Fig. 20 A).

The enamel (e) forms a fairly thick layer over the crown of the tooth; it exhibits a very clear striated structure, the striations being apparently due to stratification.

Some of the tubules of the dentine (d) continue into the enamel, where they may be distinguished by their remarkable fineness and their straight course.

The cement (c) covers the root of the tooth that projects into the alveolus of the jawbone; it is much more strongly developed than in the lizards and contains a very large number of bone corpuscles which are distinguished from the bone corpuscles proper by their greater circumference.

The fairly large pulp cavity (p) has, like the tooth itself, a conical form.

Parallel to the teeth is a row of small foramina, a continuation of those noted in the premaxilla; some or all of these foramina open into a longitudinal sinus along the alveolar border of the maxilla; this sinus opens posteriorly by one or more large apertures into the posterior palatine vacuity.

The _palatines_ (9) form a broad bar of bone from the pterygoids behind to the maxillæ in front. They are united with each other by a straight median suture and form a considerable part of the floor as well as a part of the side walls and roof of the nasal passage. They form most of the median boundaries of the posterior palatine vacuities (pv). Dorsally they articulate with the pterygoids, prefrontals, and vomers.

The _pterygoids_ (10) are the very irregular bones that project ventrad and caudad from beneath the orbits. Their suture is continuous, caudad, with that between the palatines and at the posterior end of this suture is the posterior opening of the nasal chamber, the posterior nares (pn). This opening is divided by a vertical, longitudinal, bony septum, and the part of the chamber into which it immediately opens, which lies in the pterygoids, is divided by a number of transverse, vertical septa. Posterior and dorsal to the posterior nares the pterygoids are fused. Anteriorly the pterygoids articulate with the palatines; dorsally with the quadrates, basisphenoid, alisphenoids, and prefrontals, and dorso-laterally with the transpalatines. The lateral vertical border of the pterygoid is roughened and is, according to Reynolds, covered, during life, with a pad of cartilage against which the medial side of the mandible plays.

The _transpalatine_ (11) is a T-shaped bone articulating ventrally with the pterygoid and dorsally with the maxilla, the jugal, and the postfrontal.

[Illustration: FIG. 20A. LONGITUDINAL SECTION OF THE JAW AND TOOTH OF A CROCODILE.

(After Bronn.)

_c_, cement; _d_, dentine; _e_, enamel; _p_, pulp, of functional tooth; _c′_, cement; _d′_, dentine; _e′_, enamel, of rudimentary tooth; _e″_, epidermis; _k_, bone of jaw.]

The _basioccipital_ (14) is seen projecting caudad as the single occipital condyle; it will be described in connection with the posterior aspect of the skull.

The _jugal_ (5), _quadratojugal_ (12), and _quadrate_ (8) may all be seen from this view. The first two have been sufficiently described in connection with the dorsal aspect; the last will be further described in connection with the lateral aspect.

Just caudad to the posterior nares is a small opening, the unpaired Eustachian canal (eu).

_The Lateral Aspect_ (Fig. 21). As will be seen by the figure, practically all of the bones visible in this view have already been described, except those of the mandible, which will be described separately. At the base of the skull are, however, two bones, the basi- and alisphenoid, that have not been described and that show as well in this as in any other view. The _basisphenoid_ (just below v and hidden by the pterygoid) was mentioned in connection with the quadrate, with whose posterior margin it articulates. It is an unpaired bone of very irregular shape. Anteriorly it is flattened out to form the rostrum, a rectangular process that forms the posterior part of the interorbital septum; in fact it is the only part of the septum present in a prepared skull, since the rest is cartilaginous. Dorso-laterally the basisphenoid articulates with the alisphenoid; posteriorly with the basioccipital; ventrally with the pterygoid; and posteriorly with the exoccipital and basioccipital. On the dorsal surface of the basisphenoid is the pituitary fossa, not seen, of course, in this view of the skull.

The _alisphenoids_ (crossed by the dotted line from V) are a pair of very irregular bones that form most of the antero-lateral walls of the brain case. They articulate dorsally with the parietal, frontal, and postfrontal; ventrally with the basisphenoid and pterygoid; and posteriorly with the quadrate and some of the otic bones not visible in this view. Between it and the quadrate, plainly visible in this view, is a large opening, the _foramen ovale_ (V), through which, according to Reynolds, the trigeminal nerve passes. In the middle line, directly under the frontal bone, is an opening between the anterior wings of the two alisphenoids, for the exit of the optic nerves. Ventrad and caudad to this opening, and sometimes continuous with it, is another large foramen, just dorsad to the rostrum, for the exit, according to Reynolds, of the oculomotor and abducens nerves. Projecting caudad is seen the rounded condylar part of the _basi-occipital_ (14) to be described later, and dorso-cephalad to this is a part of the exoccipital (13) in which four foramina may be seen; of the dorsal three the one nearest the condyle and foramen magnum is for the exit (Reynolds) of the hypoglossal nerve (XII); slightly dorso-cephalad to this is one for the vagus nerve (X); between these two is a very small one for a vein; the largest and ventrally located foramen is for the entrance of the internal carotid (15). Another large foramen in the exoccipital bone will be seen and described in connection with the posterior view of the skull. Dorsal to the quadrate and largely bounded by it is the wide _external auditory meatus_ (16), which leads into the tympanic cavity. This cavity is complicated by a number of canals that lead from it in various directions. Overhanging the cavity and meatus is the squamosal bone, described in connection with the dorsal aspect of the skull.

[Illustration: FIG. 21. LATERAL VIEW OF THE SKULL OF AN ALLIGATOR (_Caiman latirostris_). ×¹⁄₃. (Brit. Mus.)

(After Reynolds.)

1. premaxilla. 2. maxilla. 3. lachrymal. 4. prefrontal. 5. jugal. 6. postfrontal. 7. squamosal. 8. quadrate. 9. palatine. 10. pterygoid. 11. transpalatine. 12. quadratojugal. 13. exoccipital. 14. basi-occipital. 15. foramen by which carotid artery enters skull. 16. external auditory meatus. 17. frontal. 18. supra-angular. 19. articular. 20. dentary. 21. coronoid. 22. angular. III, VI, opening for exit of oculomotor and abducens nerves. V, foramen ovale. X, pneumogastric foramen. XII, hypoglossal foramen.]

_The Posterior Aspect_ (Fig. 22). Most of the bones seen in this view have already been described. The _pterygoids_ (10) form the two prominent, ventro-lateral projections, while dorsal to these is the large process formed by the quadrate (8) and quadratojugal (12). The dorsal margin is formed by the edges of the parietal (23) and the squamosals (7). Immediately below the parietal is the supraoccipital (26); it is a small, triangular bone, articulating above with the parietal and squamosals, below with the exoccipitals, and anteriorly with the epiotic. It takes no part in the formation of the foramen magnum.

The _exoccipitals_ (13) form the entire boundary of the foramen magnum except the narrow ventral portion formed by the basioccipital. Each exoccipital is a wing-shaped bone, articulating dorsally with the squamosal and supraoccipital, ventrally with the quadrate, basioccipital, and basisphenoid, and anteriorly with the opisthotic. It is pierced by five foramina, four of which were described in connection with the lateral view. Some distance laterad and somewhat dorsad to the pair already described is the fifth and largest foramen (VII); it really lies between the exoccipital and quadrate, but the former bone forms almost its entire boundary; through it, according to Reynolds, pass the seventh nerve and certain blood-vessels.

[Illustration: FIG. 22. POSTERIOR VIEW OF THE SKULL OF A. MISSISSIPPIENSIS.

7. squamosal. 8. quadrate. 10. pterygoid. 11. transpalatine. 12. quadratojugal. 13. exoccipital. 14. basioccipital. 15. foramen for carotid artery. 23. parietal. 26. supraoccipital. VII. foramen for 7th nerve and certain blood-vessels. _bs_, position of basisphenoid.]

[Illustration: FIG. 23. LONGITUDINAL SECTION THROUGH THE SKULL OF AN ALLIGATOR (_Caiman latirostris_). ×¹⁄₃. (Brit. Mus.) (After Reynolds.)

1. premaxilla. 2. nasal. 3. frontal. 4. parietal. 5. supra-occipital. 6. epiotic. 7. prootic. Immediately in front of the figure 7 is the prominent foramen for the trigeminal nerve. 8. opisthotic. 9. basioccipital. 10. quadrate. 11. pterygoid. 12. basisphenoid. 13. alisphenoid. 14. prefrontal. 15. vomer. 16. maxilla. 17. palatine. 18. dentary. 19. splenial. 20. angular. 21. supra-angular. 22. articular. 23. coronoid. 24. exoccipital. 25. squamosal. 26. jugal. 27. external mandibular foramen. 28. internal mandibular foramen. VIII. internal auditory meatus. XII. hypoglossal foramen.]

[Illustration: FIG. 24. DORSAL VIEW OF LOWER JAW OF ALLIGATOR (_A. Mississippiensis_).

18. dentary. 19. splenial. 21. supra-angular. 22. articular. 23. coronoid.]

The _basioccipital_ (14) which, as has been said, forms a small part of the ventral wall of the foramen magnum, consists of a heavy dorsal portion, the ventrally curved condyle, and of a broader, irregular ventral portion, between which and the basisphenoid is the single opening of the Eustachian canals (eu). Dorsally and laterally the basioccipital articulates with the exoccipitals; ventrally, laterally, and anteriorly with the basisphenoid which was described in the lateral view.

_The Sagittal Section_ (Fig. 23). The only bones shown in this figure (besides those of the mandible, to be described later) that have not already been described are the vomers and those of the auditory capsules.

The _vomers_ (15) are delicate bones articulating with the maxillæ, the palatines, the pterygoids, and with each other. They form a part of the septum and roof of the nasal passage.

The _mesethmoid_ is not ossified.

Reynolds describes the bones of the auditory capsules as follows:

“Three bones, the _epiotic_, _opisthotic_, and _pro-otic_, together form the auditory or _periotic_ capsule of each side. They are wedged in between the lateral portions of the occipital and parietal segments and complete the cranial wall in this region. Their relations to the surrounding structures are very complicated, and many points can be made out only in sections of the skull passing right through the periotic capsule. The relative position of the three bones is, however, well seen in a median longitudinal section. The _opisthotic_ early becomes united with the exoccipital, while the _epiotic_ similarly becomes united with the supraoccipital, the pro-otic (Fig. 23, 7)--seen in longitudinal section to be pierced by the prominent _trigeminal foramen_--alone remaining distinct throughout life. The three bones together surround the essential organ of hearing which communicates laterally with the deep tympanic cavity by the _fenestra ovalis_.

“The _tympanic cavity_, leading to the exterior by the _external auditory meatus_ (Fig. 21, 16), is well seen in a side view of the skull; it is bounded on its inner side by the periotic bones, posteriorly in part by the exoccipital, and elsewhere mainly by the quadrate. A large number of canals and passages open into it. On its inner side opening ventro-anteriorly is the _fenestra ovalis_, opening ventro-posteriorly the _internal auditory meatus_ (Fig. 23, VIII), while dorsally there is a wide opening which forms a communication through the roof of the brain case with the tympanic cavity of the other side. On its posterior wall is the prominent foramen through which the facial nerve passes on its way to its final exit from the skull through the exoccipital; this foramen is bounded by the quadrate, squamosal, and exoccipital. The opening of the _fenestra ovalis_ is in the fresh skull occupied by the expanded end of the auditory ossicle, the _columella_, whose outer end articulates by a concave facet with a trifid _extracolumellar_ cartilage which reaches the tympanic membrane. The lower process of this extracolumella passes into a cartilaginous rod which lies in a canal in the quadrate and is during life continuous with Meckel’s cartilage within the articular bone of the mandible.

“The columella and extracolumella are together homologous with the chain of mammalian auditory ossicles.”

_The Lower Jaw_ (Figs. 21, 23, and 24). The mandible consists of two similar rami, rather closely united at the anterior-median symphysis with each other. Each ramus consists of six bones.

The _dentary_ (Figs. 23 and 24, 18; Fig. 21, 20) is a long bone that unites at the symphysis with its fellow to form the point of the jaw. It bears, along its dorsal edge, about twenty teeth; all but the posterior four or five of these teeth are in individual sockets; this may vary somewhat with age. The outer surface of the dentary, especially towards the symphysis, is covered with numerous, small, deep pits, while along its inner side, parallel to the row of teeth, is a row of somewhat larger pits like those noted in the maxilla and premaxilla. Articulating with the mesial side of the dentary along the greater part of its length is a flat bone, the _splenial_ (Figs. 23 and 24, 19); between these two bones is a long cavity that makes the ramus hollow almost to the symphysis. A large foramen, not shown in any of the figures, leads through the splenial into this cavity.

Articulating with the caudal end of the splenial and forming the anterior border, as seen from the mesial side, of the large _external mandibular foramen_ (Fig. 23, 27) is a small bone, the _coronoid_ (Figs. 23 and 24, 23, Fig. 21, 21); it articulates with the splenial anteriorly, with the supra-angular dorso-caudally, and with the angular ventrally.

The _supra-angular_ (Figs. 23 and 24, 21, Fig. 21, 18) is an elongated bone that forms the dorsal border of the external mandibular foramen; it also forms the lateral edge of the articular surface for the quadrate. It articulates anteriorly with the splenial, the dentary, and the coronoid; and posteriorly with the angular and articular.

The _articular_ (Figs. 23 and 24, 22, Fig. 21, 19), which is scarcely visible in a lateral view, forms most of the surface for articulation with the quadrate, and sends back the large process so characteristic of the crocodilian skull. On the dorsal side of this process is a concavity that looks like another articular surface. Laterally the articular articulates with the supra-angular; ventrally and posteriorly with the angular.

The _angular_ (Fig. 23, 20, Fig. 21, 22) forms the ventro-posterior border of the jaw and of the external mandibular foramen. Its narrow, posterior end forms a part of the prominent process mentioned in connection with the articular. Between it and the posterior edge of the splenial is the _internal mandibular foramen_, which is much smaller than the external (Fig. 23, 28). Anteriorly the angular articulates with the dentary, coronoid, and splenial; dorsally with the supra-angular and the articular.

_The Hyoid_ (Fig. 25). The hyoid being mainly of cartilage is usually not seen in prepared skeletons. It is thus described by Reynolds:

“The hyoid of the Crocodile consists of a wide flattened plate of cartilage, the _basilingual plate_ or _body of the hyoid_, and a pair of _cornua_.

“The _basilingual plate_ (Fig. 25, 1) is rounded anteriorly and marked by a deep notch posteriorly. The _cornua_ (Fig. 25, 3), which are attached at a pair of notches near the middle of the outer border of the basilingual plate, are partly ossified, but their expanded ends are formed of cartilage. They pass at first backwards and then upwards and inwards. They are homologous with part of the first branchial arches of Selachians.”

[Illustration: FIG. 25. HYOIDS OF AN ALLIGATOR (_Caiman latirostris_) (TO THE LEFT) AND OF A GREEN TURTLE (_Chelone midas_) (TO THE RIGHT). ×⁵⁄₈. (Brit. Mus.) (After Reynolds.)

The cartilaginous portions are dotted.

1. basilingual plate or body of the hyoid. 2. hyoid arch. 3. first branchial arch (anterior cornu). 4. second branchial arch (posterior cornu).]

_III. The Ribs and Sternum._

_The Cervical Ribs._ As noted above, all of the cervical vertebræ possess ribs. The first rib, attached to the atlas, consists of a single, long blade projecting backward at an acute angle (Fig. 17, 8) as far as the middle of the fourth vertebra. As described above it articulates with the atlas at but one place. All of the other cervical ribs have two articular surfaces, a tuberculum and a capitulum, with a well-marked vertebrarterial canal between them. The ventral surface or capitulum articulates with a short process on the centrum; the dorsal surface or tuberculum (7) articulates with the transverse process. The third to seventh ribs are somewhat T-shaped, the stem of the T being the tubercle and head, while the cross arm of the T extends parallel to the axis of the neck (Fig. 17, 7). In the eighth rib the posterior arm of the T is elongated and projects out at a wide angle from the body; and in the ninth or last cervical rib this arm extends laterally as far as the vertebral portion of the thoracic ribs and has a cartilaginous tip.

_The Thoracic Ribs_ (Figs. 16 and 26). These are ten in number, the first eight pairs being connected with the sternum. The fourth may be taken as typical. It consists of a bony vertebral portion and partially ossified intermediate and sternal portions. The vertebral portion articulates with its corresponding transverse process by two surfaces, as described in connection with the thoracic vertebræ. In the first and second ribs only the tuberculum articulates with the transverse process, the head having a separate articular surface on the side of the centrum, as in the typical cervical rib. In the last thoracic rib the head and tubercle are not distinguishable from each other. Near the distal end of all the vertebral portions except the first and the last two ribs is a caudally projecting, partially ossified, uncinate process. The intermediate portion is present in all but the tenth rib, and wherever present, except in the ninth rib, it articulates distally with the sternal portion. The sternal portions extend medio-cephalad in a direction at right angles to the intermediate portion; the first two articulate with the sternum, the next six with the xiphisternal horns, and the ninth and tenth are missing.

[Illustration: FIG. 26. STERNUM AND ASSOCIATED MEMBRANE BONES OF A CROCODILE (_C. palustris_). ×¹⁄₃. (Brit. Mus.) (After Reynolds.)

The last pair of abdominal ribs which are united with the epipubes by a plate of cartilage have been omitted.

1. interclavicle. 2. sternum. 3. sternal rib. 4. abdominal splint rib. 5. xiphisternal horn.]

_The Abdominal Ribs_ (Fig. 26, 4). While these ribs are membrane bones and are not homologous with the other ribs, they may as well be mentioned at this time. They consist of about seven V-shaped sets of slender bones, the point of each V being directed cephalad. Each V is made up of from two or five slender bones, the number and arrangement being subject to considerable variation. The last V of the series (not well shown in the figure) is considerably larger than the rest and is made up of four curved bones that extend around the anterior ends of the pubic bones and are united to them by a broad tough membrane. The first or most anterior V is united by a narrow membrane (not shown in the figure) with the membrane that extends between the xiphisternal horns. All of the V’s are more or less connected with each other by fibrous membranes. Since these ribs lie superficial to the recti muscles of the ventral body wall they are sometimes missing in carelessly prepared skeletons.

_The Sternum_ (Fig. 26). The sternum consists of the cartilaginous sternum proper (2), the xiphisternal horns (5), and the bony episternum or interclavicle (1). The latter is an elongated, flattened bone of somewhat spatulate outline, lying in the midventral line; it projects forwards to about the sixth cervical vertebra, while the anterior edge of the sternum is below the eighth cervical. Lying dorsal and lateral to the episternum is the flat, almost membranous sternum, to the posterior border of which the first two thoracic ribs are attached. The xiphisternum consists of two long, slender rods of cartilage; the anterior ends of these rods are in contact with each other and with the posterior border of the sternum; from this point they gradually diverge from each other as they extend caudad. A membrane extends between the horns as far back as the attachment of the last thoracic ribs.

_IV. The Appendicular Skeleton._

_The Pectoral Girdle_ and _Anterior Limb_. The pectoral girdle (Fig. 27) is of a very simple type, consisting, unless the episternum (interclavicle) be counted, of but two bones, the _scapula_ (_s_) and _coracoid_ (_c_). The former consists of an upper, flat, paddle-shaped portion and a thicker lower portion which articulates anteriorly with the coracoid, and posteriorly forms about half of the notch-like glenoid cavity. The dorsal edge of the flattened portion is continued as a small, cartilaginous suprascapula. The coracoid is a flattened bone, wide at either end and narrow in the middle, so that in a dorsal view it is shaped like an hourglass. It is decidedly curved, with the convex side down. Its outer edge articulates with the scapula and is thickened to form the anterior border of the glenoid cavity. Its median end is attached to the sternum. Near its scapular articulation there is a well-marked foramen that passes entirely through the bone. The _episternum_ (_e_) or interclavicle was described in connection with the sternum and ribs. There is no clavicle nor other coracoid elements.

[Illustration: FIG. 27. PECTORAL GIRDLE AND ANTERIOR LIMB.

_c_, coracoid; _ce_, centrale; _cl_, claw; _e_, episternum; _h_, humerus; _m_, metacarpals; _p_, pisiform; _r_, radius; _r′_, radiale; _s_, scapula; _u_, ulna; _u′_, ulnare.]

The _anterior limb_ consists of the usual parts,--the upper arm, forearm, and manus. The _humerus_ (Fig. 27, _h_) is rather thick in proportion to its length; it has an elongated articular surface at its proximal end for articulation with the glenoid cavity, and a larger, somewhat bilobed surface for articulation with the radius and ulna. On its ventral side, near the proximal end, is a very prominent protuberance, the deltoid ridge. The _ulna_ (_u_) is slightly heavier and longer than the radius and forms the greater part of the elbow joint and about half of the wrist joint. Its proximal end is considerably larger than the distal, but has no olecranon process. Its distal end articulates with the ulnare and pisiform. The ulna as a whole is slightly curved, while the radius is quite straight.

The _radius_ (_r_) consists of a cylindrical shaft with enlargements of about equal size at the ends. The proximal end articulates with the side of the ulna and with the humerus; the distal end with the radiale.

The carpus consists of a proximal row of three distinct bones and a distal row of smaller and less fully ossified elements. Of the proximal row the _radiale_ (_r′_) is much the largest bone. It is hourglass shaped, with the proximal end somewhat larger than the distal. Proximally it articulates mainly with the radius but also slightly with the ulna and ulnare. Distally it articulates with the centrale. The _ulnare_ (_u′_), the second bone in size in the wrist, has about the same shape as the radiale but is much smaller. Proximally it articulates with the pisiform, radiale, and, apparently, with the ulna; distally it is in contact with the fused carpalia elements. The _pisiform_ (_p_) is a small, irregular bone, articulating with the ulna and the ulnare; it is apparently connected by a long ligament with the fifth metacarpal but does not actually articulate with it. The _centrale_ (_ce_) is a flattened, partially ossified element between the radiale and the first and second metacarpals. The distal carpal bones are represented by two irregular, partially ossified elements between the ulnare and the third, fourth, and fifth metacarpals.

The manus proper consists of five digits. The _metacarpals_ (_m_) are of about the same shape, but vary in length and thickness; each consists of a cylindrical shaft with a slight enlargement at each end. The first digit or pollex has two phalanges, the second has three, the third has four, the fourth has four, and the fifth has three. The terminal phalanx of each of the first four digits is pointed, has a pair of lateral grooves, and is encased in a large, horny _claw_ (_cl_).

_The Pelvic Girdle_ and _Posterior Limb_. The pelvic girdle is described differently by Wiedersheim and Reynolds; the bone called by the former the pubis, the latter calls the epipubis. The bone called by Wiedersheim the pubis takes no part in the formation of the acetabulum; the pubis of Reynolds helps form the acetabulum but is a very small, unossified structure. Gadow also calls the lower bone the epipubis. I shall follow Reynolds’s interpretation.

The _ilium_ (Fig. 28, 1) is a heavy bone with a dorso-laterally projecting crest; medially it is firmly united to the sacral ribs (Fig. 18, 5) while its outer side forms the upper and greater part of the acetabulum. Its outer and lower border has two surfaces, the larger and more posterior articulating with the ischium, the other with the cartilaginous pubis.

[Illustration: FIG. 28. PELVIS AND SACRUM OF AN ALLIGATOR (_Caiman latirostris_). ×¹⁄₂. (Brit. Mus.) (After Reynolds.)

1. ilium. 2. ischium. 3. true pubis. 4. epipubis (so-called pubis). 5. acetabular foramen. 6. neural spines of sacral vertebrae. 7. symphysis ischii. 8. process bearing prezygapophysis.]

The _ischium_ (2) is a slightly arched bone, its ventral end a flattened blade articulating with its fellow, its dorsal end enlarged and thickened to articulate with the ilium, pubis, and epipubis. This dorsal end, which forms the ventral side of the acetabulum, is divided into two distinct articular surfaces by a deep, rounded notch; the posterior and larger surface articulates with the ilium, the anterior surface about equally with the pubis and epipubis.

The _pubis_ (3), which is much the smallest element of the pelvis, is a small mass of cartilage lying between the ilium above and the ischium below. It forms a small part of the anterior wall of the acetabulum.

The _epipubis_ (4) is a slightly arched bone, somewhat enlarged at its proximal end where it unites with the ischium, and flattened out into a fan-shaped extremity, where it is united with its fellow and with the last pair of abdominal ribs by the broad, thin sheet of cartilage or fibrous tissue noted in connection with the abdominal ribs. As mentioned above, it is called by Wiedersheim and others the pubis. Near the center of the acetabulum there is a small foramen.

The _posterior limb_ (Fig. 29) consists of the usual divisions--thigh, shin, and foot. The _femur_ (f) is a bone of the same general outline as the humerus, though slightly longer and heavier. The head, for articulation with the acetabulum, is rather hemi-elliptical than hemispherical in shape, the long axis of the ellipse being vertical. The distal enlargement is of at least as great, if not greater, bulk than the proximal and shows some indication of a division into two articular surfaces. The ventral side of the femur near the proximal end shows a fairly distinct trochantal ridge.

The shin or crus is made up of two well-developed bones, the _tibia_ (t) and _fibula_ (fb), the former being somewhat longer and considerably thicker than the latter.

[Illustration: FIG. 29. POSTERIOR LIMB.

_ca_, calcaneum or fibulare; _cl_, claw; _f_, femur; _fb_, fibula; _t_, tibia; _t³_, _t⁴⁻⁵_, tarsalia; _tb_, _tb′_, tibiale-centrale; _IV_, _V_, 4th and 5th metatarsals.]

The tibia consists of a cylindrical shaft with enlargements of about equal size at the ends. The proximal end forms most of the knee joint, the distal end articulates with a tarsal element said by Reynolds to represent the fused astragalus and centrale, by Wiedersheim called the astragalus, and said to represent the united tibiale, intermedium, and centrale (tb, tb′). The fibula articulates by a small enlargement at its proximal end with the femur, and by an enlargement of about equal size, at its distal end, with the fibulare or calcaneum (ca), and with a small facet on the above-mentioned tibiale-centrale element.

The tarsus is much modified and consists of four elements, in two rows; those of the proximal row are much larger than the two distal elements. Articulating with both tibia and fibula, as mentioned above, and with the first metatarsal and one of the distal tarsalia, is the large and irregular _tibiale-centrale_ element of Reynolds (tb, tb′). In the tarsus here shown it consists of two elements. Post-axial in position is the _calcaneum_ or _fibulare_ (ca), articulating with the preceding tarsal element, with the fibula, with the rudimentary fifth metatarsal, and with the distal tarsal element said by Reynolds to represent the fourth and fifth tarsalia. The calcaneum is extended caudad into a prominent knob quite like the heel of the higher mammals.

The two distal tarsal bones are small; one is said by Reynolds to represent the first three _tarsalia_ (t³), the other (t⁴⁻⁵) the fourth and fifth. Wiedersheim says one of these bones represents the first three tarsalia, the other the fourth. In the tarsus here shown these two elements are fused.

The foot has five digits, though the fifth is small and consists merely of a small, distally pointed metatarsal bone. According to Wiedersheim this fifth metatarsal is fused with the fifth tarsalia. The metatarsals of the first four digits are long and progressively more slender from the first to the fourth; each is distinctly enlarged at the ends. The first digit or hallux has two phalanges, the second has three, the third has four, and the fourth has four. According to Reynolds, the fourth toe has five phalanges; the figure here shown, which was drawn from nature, has only four on the fourth toe; the latter is the number given by Bronn for the crocodiles. The terminal phalanges of the first three digits are large and pointed, with the same lateral grooves noted in connection with the fore foot; each is sheathed in a horny claw. The four fully developed digits of the pes are nearly twice as long as the corresponding digits of the manus, but they are not proportionately thicker.

Chapter III

The Muscles

The description of the muscles here given is taken from Bronn (11), who, in turn, largely follows Gadow. The animal described is the crocodile, but while Bronn does not indicate the species, it is probable that the differences between the various members of the Crocodilia would be slight. The figures of the muscular system are mainly from the Florida alligator.

In his description Bronn gives for each muscle the various synonyms (often more than half a dozen) that are employed by different writers; in this work Bronn’s nomenclature is given first and the synonyms follow in parentheses.

The Chewing Muscles

_Temporalo-maxillaris_ (Temporalis) (Masseter, Temporal, Aeussere ober Heber or Schlafmuskel). Arises in the temporal fossa, passes under the zygoma, and inserts itself on the inner and outer sides of the lower jaw.

_Pterygo-maxillaris_ (Pterygoideus) (Pterygoidien, Aeusser Flügelmuskel, Pterygoideus externus, Pterygoideus internus). A large muscle which consists of two portions: the outer, weaker portion springs from the pterygoid process, the inner stronger part from the pterygoid fossa and pterygoid process; they run together around the angle of the lower jaw, where they form a large, bulging fold. They are the chief muscles of this part of the body since the masseter is lacking and the temporalis is weakly developed.

_Occipito-maxillaris_ (Digastricus maxillæ) (Niederzieher des Unterkiefers, Abaisseur ou l’analogue du digastrique, Senker des Unterkiefers, Aristotelis apertor oris, Digastricus, Aperator oris). Arises from the hinder border of the lateral occipital and is inserted at the hinder end of the lower jaw. Its course is from front to back. If the skull be stationary this muscle drops the lower jaw; if the jaw be fixed it raises the skull.

Muscles Of The Ventral Surface Of The Neck

_Intermaxillaris_ and _Sphincter Colli_ (Intermaxillaire, Mylo-hyoideus, Zwischenkiefermuskel, Latissimus colli). This muscle consists chiefly of transversely running fibers, and has in its middle third a small, median, longitudinal raphe or aponeurosis. In the posterior part of the neck it is very thin, but increases in thickness more and more as it passes cephalad. A short anterior and a long posterior portion may be distinguished. The former extends from the inner side of the right to that of the left half of the lower jaw, without a median aponeurosis. The hinder half of this muscle is united by a pair of aponeuroses to the lower jaw, on one hand (the smaller part), and to a fascia, on the other hand (the far larger part), that separates several of the neck muscles. The smaller part begins immediately behind the pterygoid on the inner side of the halves of the lower jaw but ends on the outer side of the two halves of the jaw.

_Latus Colli_ (Latissimus colli accessorius). Lies underneath the preceding. Its muscle bundles lie between the collo-capitis muscle and the bodies of the first three cervical vertebræ, and form a broad band that extends from the hyoid bone to the backwardly directed cervical ribs of the first and second pairs.

_Coraco-ceratoideus_ (Omo-hyoideus, Coraco-hyoideus). A long, narrow, and moderately thick muscle which takes its origin from the upper border of the coracoid, where the latter touches the scapula. It extends forward near the œsophagus and attaches itself to about the middle of the backwardly turned border of the horn of the hyoid of that side.

_Episterno-ceratoideus_ (Niederzieher des Zungenbeins, or Brustbeinzungenbeinmuskel, Sterno-hyoideus). A flat and fairly broad muscle which springs from the ventral surface of the episternum; behind, it is separated by a slight space from the corresponding muscle of the other side, with which it nearly covers the cervical part of the trachea. Towards its anterior end it divides into two heads; one of these inserts itself on the outer border and outer surface of the cornu of the hyoid; the other head, lying laterad to the former, is suddenly reduced to a short tendon by which it is attached to the following muscle.

_Maxillo-coracoideus_ (Mylo-hyoideus anterior, Sterno-maxillare). This muscle arises from the upper border and inner surface of the caudal third of the lower jaw. In its further course it becomes tendinous and projects by a short tendon outwards from the hyoid cornu to unite with the head of the preceding muscle, as noted above; it then becomes fleshy again and is inserted on the medial part of the upper border of the coracoid.

_Maxillo-hyoideus_ (Genio-ceratoidien, Hyomaxillaris, Hyoglossus, Hyomandibularis, Mylo-hyoideus posterior). This muscle arises, very thin, from the mandibular symphysis, goes thence immediately backward and inward to insert itself, by its broad end, on the whole anterior end of the horn of the hyoid and on the hyoid itself.

_Cerato-hyoideus._ Arises from the horn of the hyoid and inserts itself on the body of the hyoid.

_Costo-coracoideus._ This muscle arises from the distal ends of the first and second ribs and is inserted on the ventral surface of the coracoid at the boundary of the scapula.

_Costo-scapularis_ (Collo-scapularis superficialis, Levator scapulæ superficialis). See shoulder muscles.

_Costo-vertebralis Medialis_ (Scaleni). Fairly large, flat, and long-drawn-out three-cornered muscle. Attached by its base to the most anterior sternal rib, by its upper border to the fifth cervical rib, and by its point to the end of the second cervical rib.

_Costo-vertebralis Lateralis_ (Longus colli). Originates thin and sharp on the body of the fifth thoracic vertebra, increases in thickness slowly but decidedly cephalad, then again becomes thinner and inserts itself on the inner side of the ribs of the most anterior two cervical vertebræ.

_Collo-capitis_ (Rectus capitis anterior). Arises, as a rule, from the cervical centra, at times from the second thoracic vertebra (Gavialis). It extends forward and is inserted on the basi-occipital and the hinder border of the pterygoid. For a greater part of their length the two muscles lie close together, but forward they separate somewhat from each other.

Dorsal Neck Muscles

_Occipito-cervicalis Medialis_ (Complexus cervicis, Biventer cervicis, Zweibäuchiger Strecker or Zweibäuchiger Nackenmuskel, Splenius capitis). It springs, by separate points, from the dorsal processes of the four anterior body vertebræ and the six posterior neck vertebræ; it is convex on its dorsal, weakly concave on its ventral surface; it leads cephalad as a short, strong tendon by which it is attached to the angle between the upper hinder border of the skull, _i.e._ to the superior and lateral occipital region.

_Squamoso-cervicalis Medialis_ (Kopfbäuchmuskel [Splenius] or durchflochtener Muskel [Complexus], Trachelo-mastoideus, Complexus). This muscle lies laterad and ventrad to the preceding and is at times partly covered by it in its posterior half. It arises from separate heads from the spinal processes of the two anterior and six posterior cervical vertebræ; beginning caudad, thin and sharp, it gradually becomes thicker as it passes cephalad until it becomes partially tendinous and inserts itself on the hinder border of the squamosal, laterad to the occipito-cervicalis medialis muscle.

_Epistropheo-vertebralis_ (Splenius colli). This muscle springs from the spinous processes of the most anterior three body vertebræ and the last cervical vertebra; it receives fibers from the articular processes and intermediate parts of the six posterior cervical vertebræ and is inserted on the second cervical vertebra.

_Collo-squamosus_ (Splenius capitis, Nackenwarzenmuskel, Trachelo-mastoideus). Springs from the upper transverse processes of the last three neck vertebræ, and, becoming tendinous, is inserted on the hinder border of the squamosal.

_Collo-occipitis._ Arises from the transverse processes of the posterior five cervical vertebræ, extends directly forwards on the ribs of the vertebræ, and is inserted under the articular surface of the lateral occipital.

_Occipito-epistropheus_ (short, straight, hinder head-muscle, or extensor). This muscle springs from the lateral surface of the body of the second neck vertebra and inserts itself on the basi-exoccipital, under the preceding muscle.

_Cervicalis Adscendens._ Arises in great part from the angles under the most anterior ribs; a smaller part appears farther above where it is covered by the rhomboideus muscle. It is inserted on the upper side of the five posterior cervical ribs and on the distal ends of the long second cervical rib.

The Muscles Of The Scapula

_Capiti-sternalis_ (Sterno-mastoideus). This is a fairly large muscle, on the side of the neck, that extends from the skull to the breast and from the middle of the neck is divided into two portions: (a) an anterior part or atlanti-mastoideus (Plate I., Figs. 1 and 2, cst¹) (upper end of the “head nodder,” sterno-mastoideus, anterior part of sterno-mastoideus, anterior part of atlanti-mastoideus); (b) a posterior part or sterno-atlanticus (Plate I., Figs. 1 and 2, cst²) (sterno-mastoideus, inner belly of the “head-nodder,” posterior part of the sterno-atlanticus). The former part is a rather short but not weak muscle that arises from the squamosum and inserts itself on the rib of the atlas (alligator) or of the atlas and epistropheus (crocodile).

The latter part is fairly strong and exceeds the anterior part in length; it springs from the rib of the first cervical vertebra, opposite the insertion of the anterior part, and inserts itself on the anterior border of the outer surface near the episternum. At times superficial fibers pass into the pectoral fascia.

_Dorso-scapularis_ (Cucullaris) (Plate I., Figs. 1 and 2, Cu) (Trapezius). A broad but thin muscle that begins as an aponeurosis from the dorsal fascia in the middle line of the hinder part of the neck and beginning of the back; with converging fibers it passes within to insert itself partly on the spine of the scapula and partly by superficial fibers in the fascia that cover the deltoides scapularis inferior muscle.

_Collo-scapularis Superficialis_ (Plate I., Fig. 1, cssp) (Levator scapulæ superficialis, Levator scapulæ, Heber des Schulterblatts, Acromio-trachélien, Teil des Serratus magnus, Levator anguli scapulæ). A considerable muscle on the side of the neck. It arises from the tips of the ribs of the first and second cervical vertebræ (where it is fused with the sterno-atlanticus muscle), and also from the transverse process of the third and fourth cervical vertebræ; it goes with diverging fibers to the entire anterior border of the scapula.

_Thoraci-scapularis Superficialis_ (Serratus superficialis, Pectoralis minor, Hinterer Theil des inneren grösseren Rückwärtsziehers, Pars posterior m. serrati antici majoris, Theil des Grand dentelé, Serrati posteriores, Latissimus dorsi scapulo-costalis). A strong muscle of three prongs that go directly, by superficial fibers, over into the oblique abdominal muscle and meet the ribs. The first and smallest prong arises from the under end of the rib of the ninth vertebra (last cervical); the second and medium-sized prong comes from the uncinate process of the tenth rib (first thoracic) and from beneath the uncinate process of the second thoracic rib; the third and strongest prong takes its origin from the uncinate processes of the second and third thoracic ribs. All three prongs unite to form a broad, homogeneous muscle which passes forward and above to the hinder border of the scapula, upon whose entire surface, except at the lower end, it is inserted.

_Collo-thoraci-suprascapularis Profundus_ (Plate I., Fig. 3, cthspr) (Levator scapulæ et serratus profundus, Serrati anteriores, Serratus anticus major, Vorderer Theil des inneren grösseren Rückwärtsziehers or vorderen grossen gezahnten Muskels, Pars anterior m. serrati antici majoris, Theil des Grand dentelé, Theil des Serratus magnus). This muscle arises in varying extent from the transverse process of the fifth cervical vertebra to the first (crocodile) or second (alligator) ribs. It is inserted on the inner surface of the suprascapula, except on its forward part, and is made up of two layers--a superficial and a deep one. The former layer (Fig. 3, cthspr¹) is weakly developed and is composed of two or three thin, distinct bundles, that extend from the ribs of the eighth, ninth, and eleventh vertebræ (alligator) or from the transverse process of the seventh vertebra and the rib of the tenth. The deeper layer is considerably developed; its bundles come, in the alligator, from the fifth to tenth vertebræ; in the crocodile from the fifth to ninth.

_Rhomboideus_ (Plate I., Fig. 3, rh) (Rautenmuskel, Angulaire de l’omoplate). This is a very small, independent muscle that springs, by two or three distinct bundles, from the fascia covering the longissimus dorsi muscle, in the region of the eighth and ninth vertebræ; after a short course it inserts itself on the antero-dorsal angle of the suprascapula.

_Costo-coracoideus_ (Plate I., Fig. 3, cc) (Subclavius et Triangularis sterni and Levator secundæ superioris costæ, Petit dentelé, Pectoralis minor, Pectoralis). This is a broad muscle of considerable size on the ventral side of the breast; it consists of a lateral and of a medial portion, the former springing from the last cervical rib, the latter from the anterior border of the first sternocostal ridge. The two parts unite and are inserted on the whole posterior border of the coracoid.

_Pectoralis minor_ (Pectoralis, Costo-coracoideus). A broad, considerable muscle on the under side of the breast, which is made up of two parts, of which the lateral springs from the anterior border of the last (ninth) cervical rib, and the medial from the anterior border of the first sternocostal ridge. Both parts unite into a homogeneous layer which is inserted broadly on the whole hinder border of the coracoid.

_Pectoralis_ (Plate I., Figs. 1 and 2, p) (Pectoralis major, Grosser Brustmuskel). A broad muscle on the under side of the breast, bounded behind by the rectus abdominis and obliquus abdominis externus muscles, with which it is united. It arises from the whole episternum, from the whole sternum, except from the median line of its posterior part, from the sternal ends of the first six thoracic ribs, from all six sternocostal ridges, and, with a small prong, from the eighth rib. It is inserted on the distal part of the convex surface of the processus lateralis humeri.

_Supracoracoideus_ (Plate I., Figs. 1 and 2, spc) (Supracoracoscapularis, Deltoideus, Schlüsselbeinhälfte, Theil der Schulterblatthälfte des Hebers des Armes, Obergrätenmuskel, Hebemuskel des Oberarmes, Epicoraco-humeralis). A muscle of considerable size at the anterior region of the coracoid and the under region of the scapula, which is divided into two parts: (a) the coracoid (inferior) division is the stronger and arises from the whole anterior half of the coracoid, from its outer and inner surfaces; it is inserted, together with the second part, on the proximal, little-developed part of the processus lateralis humeri; (b) the scapularis (superior) division is the weaker of the two and is covered by the deltoides scapularis inferior muscle; it arises from the surface of the under third of the scapula, behind the spine; it unites with the preceding part to form a single muscle and inserts itself, as said above, on the proximal part of the processus lateralis humeri.

_Coraco-brachialis_ (Brevis) (Plate I., Figs. 4, 5, and 6, cbb) (Theil des grossen Brustmuskels oder Hakenarmmuskel, Pectoralis II., Pectoralis minor). A fairly strong muscle. It arises from the outer surface of the coracoid, except the median edge and the anterior section, and runs to the flexor surface of the upper arm where it is inserted on the proximal third between the lateral and median processes.

_Coraco-antebrachialis_ (Plate I., Figs. 2 and 5, b¹) (Biceps, Coracoideus, Langer Kopf des langen Beugers, Langer Kopf des Biceps, Biceps humeri, Biceps brachii, Coraco-radialis). A slender and rather weak muscle on the flexor side of the upper arm. It arises by a fairly bro

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