The anatomy of the domestic fowl

_By_ B. F. Kaupp, M. S., D. V. M.

Poultry Investigator and Pathologist in the North Carolina Experiment Station, State Department of Agriculture, and the State College of Agriculture; Formerly Director of Anatomy Laboratory, Kansas City Veterinary College

Illustrated

_Philadelphia and London_ W. B. Saunders Company 1918

Copyright, 1918, by W. B. Saunders Company

Printed In America

To DAN T. GRAY, B. S., A. B., M. S. CHIEF, ANIMAL INDUSTRY DIVISION, NORTH CAROLINA EXPERIMENT STATION AS A TOKEN OF RESPECT AND GRATITUDE THIS VOLUME IS DEDICATED BY THE AUTHOR

Foreword

Advanced work in the study of poultry husbandry is now being done in this country, to a greater or less extent, at all the two score and more Agricultural and other Colleges and Experiment Stations. From these institutions comes the demand for a text-book on the Anatomy of the Domestic Fowl. No complete text-book on the subject, up to the present, has existed. It is with the hope of meeting the demand that this book is published.

In supplementing the information gathered from the books and articles listed in the bibliography, the author has spent much time and effort in obtaining the matter here presented. As this, however, is the initial complete text on the subject necessarily much remains to be added and corrected. The author would welcome suggestions and corrections from any one into whose hands the book may come.

B. F. Kaupp.

THE NORTH CAROLINA STATE COLLEGE OF AGRICULTURE, WEST RALEIGH, NORTH CAROLINA, _September, 1918_.

Contents

Osteology

PAGE OSSEOUS STRUCTURE 17 CLASSIFICATION OF BONES 20 COMPOSITION OF BONE 21 SKELETON OF THE FOWL 21 Axial Skeleton 23 Cranium and Face 23 Occipital 25 Ethmoid 27 Sphenoid 28 Frontal 29 Parietal 29 Temporal 29 Premaxilla 31 Maxilla 32 Nasal 32 Lacrimal 32 Palatine 33 Pterygoid 33 Zygomatic 33 Vomer 33 Jugal and Quadrato-jugal 33 Quadrate 34 Inferior Maxilla 34 Turbinate Bones 34 Hyoid 35 Vertebral Column 35 Cervical Vertebræ 35 Atlas 37 Axis 37 Dorsal Vertebræ 39 Lumbo-sacral Vertebræ 39 Coccygeal Vertebræ 41 Ribs 41 Sternum 42 Appendicular Skeleton 43 Shoulder Girdle 43 Fore Limb 44 Pelvic Girdle 48 Hind Limb 50

ARTHROLOGY KINDS OF JOINTS 56 MOVEMENTS OF JOINTS 56 LIGAMENTOUS STRUCTURE 57 LIGAMENTS OF: Ear 58 Jaw 58 Vertebræ 58 Ribs 59 Sternum 59 Shoulder-joint 61 Elbow-joint 61 Carpal Joint 62 Finger 64 Pelvis 65 Hip-joint 65 Knee-joint 65 Tibio-metatarsal Joint 69 Toes 69

MYOLOGY KINDS AND STRUCTURE OF MUSCLES 70 FASCIA 71 MUSCULAR NOMENCLATURE 71 True Dermal Muscles 71 Dermo-osseous Muscles 73 Muscles of the Head 76 Muscles of the Tongue 79 Cervical Muscles 81 Muscles of the Air Passages 86 Superior Larynx 86 Inferior Larynx 86 Sternal Muscles 90 Abdominal Muscles 90 Dorsolumbar Muscles 92 Coccygeal Muscles 93 Costal Muscles 96 Anterior Pectoral Muscles 99 Pectoral Muscles 100 Muscles of the Scapular Region 101 Muscles of the Brachial Region 104 Muscles of the Forearm and Hand 105 Digital Muscles 109 Muscles of the Posterior Limb 111 Tibial Group of Muscles 117 Muscles of the Eye 124 Muscles of the Ear 128 FUNCTIONS OF MUSCLES 128

SPLANCHNOLOGY DIGESTIVE APPARATUS 135 Mouth 135 Tongue 139 Pharynx 141 Glands Adjacent to Mouth and Pharynx 141 Esophagus 142 Crop 142 Stomach 143 Proventriculus 143 Gizzard 145 Small Intestine 147 Large Intestine 150 Cæca 151 Cloaca 151 COURSE OF THE FOOD 152 ACCESSORY ORGANS OF DIGESTION 152 Liver 153 Pancreas 155 Spleen 155 ABDOMINAL AND PELVIC CAVITIES 156 PERITONEUM AND MESENTERY 156 RELATIONS OF THE VISCERAL ORGANS OF THE DOMESTIC FOWL 158 RELATIONS OF THE VISCERAL ORGANS OF THE BABY CHICK 165 URO-GENITAL SYSTEM 169 Urinary Apparatus 169 Kidneys 169 Ureter 174 Male Generative Organs 175 Testicles 175 Vas Deferens 178 Female Generative Organs 178 Egg 180 Oviduct 182 Parts of the Oviduct 183 Ligaments of the Oviduct 188 DUCTLESS GLANDS 190 Thyroid Gland 190 Thymus Gland 190 Adrenal Gland 191 RESPIRATORY APPARATUS 193 Nostrils and Nasal Chambers 193 Pharynx and Superior Larynx 193 Trachea 194 Inferior Larynx 194 Bronchi and the Lungs 195 Air-sacs 199

ANGIOLOGY CIRCULATORY APPARATUS 206 Heart 206 Structure of the Heart 207 Blood-vessels 209 Structure of the Capillaries and Arteries 209 Structure of the Veins 211 Arterial Trunks 211 Branches of: Arteria Brachiocephalica 213 Arteria Carotis Cerebralis Interna 214 Arteria Carotis Externa 214 Arteria Carotis Facialis 214 Aorta Posterior 224 Venous Trunks 233 Branches of: Venæ Cavæ Anteriores 234 Vena Jugularis 237 Vena Occipitalis Externa 239 Venous Sinuses of the Head 239 Veins of the Brain Cavity 241 Veins of the Neck 242 Branches of the Vena Subclavia 243 Veins of the Dorsal Region 243 Veins of the Thorax 244 Veins of the Fore Limb 245 Branches of the Iliaca 246 Branches of the Vena Iliaca Interna 247 Posterior Vena Cava 247 Veins of the Posterior Extremity 248 Branches of the Vena Cava Posterior 248 Veins of the Caudal Region and Pelvic Cavity 250 Veins of the Truncus Vena Iliaca Communis 252 Visceral Veins of the Posterior Vena Cava 252 Lymphatic System 254 BLOOD AND ITS FUNCTIONS 257 FATE OF THE ERYTHROCYTE 261

NEUROLOGY NERVOUS SYSTEM 264 Cranial Nerves 265 Olfactorius 265 Opticus 267 Motoris Oculi 267 Patheticus 268 Trifacialis 268 Abducentes 270 Facialis and Acousticus 271 Vagus Group 272 Glosso-pharyngeus 272 Vagus or Pneumogastricus 273 Accessorius Spinalis 274 Hypoglossus 274 Spinal Cord 275 Structure of the Cord 275 Structure of the Nerve Trunks and Ganglia 277 Spinal Nerves 281 Brachial Plexus 282 Lumbo-sacral or Crural Plexus 285 Brain 288 Coverings of the Brain 288 Structure of the Brain 289 Divisions of the Brain 290 Sympathetic Nervous System 297 Functions of the Nervous System 300

ESTHESIOLOGY SENSE ORGANS 303 Sight 303 Hearing 305 Smell 307 Taste 307 Touch 307 STRUCTURE OF APPENDAGES 309

EMBRYOLOGY SPERMATOGENESIS 318 OÖGENESIS 319 FERTILIZATION 319 OUTLINE FOR LABORATORY STUDY OF THE CHICK 330 Living Embryo 330 Preparation for Study of Entire Embryos and Sections 330 Points to be Observed in the Study 332 DERIVATIVES OF THE GERM-LAYERS 342 PREPARATION OF STRUCTURES FOR STUDY 343 Directions for Dissecting Muscles 343 Directions for Study of the Viscera 344 Directions for Study of the Arteries 345 Study of the Structure of Bones 346 Special Technic for Dissection of Cranial and Spinal Nerves 347 Directions for Study of Soft Structures 347 To Stain Sections of Liver for Study of Kupffer Cells 349 To Prepare Anatomical Specimens for Museum 349 To Make Specimens Transparent 350 EQUIPMENT FOR THE DISSECTION LABORATORY 351

BIBLIOGRAPHY 353 ─────────────────────────────────────────────────────────────────── INDEX 355

Anatomy Of The Domestic Fowl

Osteology

=Osseous Structure.=—Bone is structurally modified connective tissue which has become hard by being impregnated with calcium salts.

_Kinds of Bone Tissue._—There are two kinds of bone tissue: substantia compacta, or compact bone tissue; and substantia spongiosa, or spongy, cancellous bone tissue.

_Compact Bone Tissue._—The compact bone tissue forms the hard outer layer of all bones. It is thickest in the shaft and becomes thin toward the extremities. Through the compact bone tissue approximately parallel with the longitudinal axis of the bone, run canals called _Haversian canals_, through which pass blood and lymph vessels for the nourishment of the bone and nerves. The Haversian canals are surrounded by _concentric lamellæ_. The spaces between the cylinders thus formed are filled with _interstitial lamellæ_; and both the exterior surface of the bone and the interior surface surrounding the medullary canal, are built up of peripheral, or circumferential lamellæ. Between the lamellæ, somewhat irregularly placed, are minute reservoirs, called _lacunæ_, which contain bone corpuscles. From the lacunæ radiate minute canals, or _canaliculi_, which maintain circulation through the bone substance, and which communicate with the Haversian canals. Complex anastomoses exist among the canaliculi. Still other channels for the passage of blood-vessels are Volkmann’s canals which pierce the peripheral lamellæ, thus allowing vessels to pass from the periosteum to the Haversian canals. Similar channels afford communication between the inner Haversian canals and the medullary cavity.

The entire structure composed of an Haversian canal, its surrounding lamellæ, lacunæ, and canaliculi, with their contained vessels, is called an _Haversian system_.

_Cancellous Bone Tissue._—The cancellous bone tissue forms the bulk of the short, flat, and irregular bones and of the extremities of the long bones. It consists of delicate bony plates and spicules, which intercross in various directions. The spaces between these plates and spicules, called _cancelli_, are occupied by marrow except in the bones that are pneumatic. The blood-vessels, lymphatics, and nerves course through this marrow but are not arranged in an Haversian system.

[Illustration:

FIG. 1.—Longitudinal section of compact bone of the femur of the hen. 1, Haversian canals. 2, Lacunæ with their canaliculi. ]

_The Periosteum._—Covering the surface of bone, except at the articular surface where it is covered with cartilage, is a membrane, the periosteum, which consists of two layers: an outer, fibrous, protective layer, and an inner, cellular, osteogenic layer. The outer layer consists principally of white fibrous tissue. The inner layer contains many more connective-tissue cells, which gradually become more closely aggregated as we proceed toward the osseous surface; but there is no sharply defined line of demarcation between the two periosteal layers.

[Illustration:

FIG. 2.—Transverse section of compact bone of the femur of the hen. 1, The lacunæ and canaliculi. 2, The periosteum. ]

[Illustration:

FIG. 3.—Transverse section of compact bone of the femur of the hen showing the lacunæ and canaliculi under high magnification. ]

The periosteum is firmly attached to the bone by trabeculæ of fibrous tissue, called the _fibers of Sharpey_. These fibers of Sharpey penetrate the bone at right angles to its surface and carry blood-vessels.

_Marrow._—There are two kinds of marrow: yellow, or medulla ossium flava, and red, or medulla ossium rubra.

The _yellow marrow_ occurs in all bones except the femur and proximal portion of the tibia of adult fowls. It is composed of a network of fibrous tissue carrying blood-vessels, fat cells, and myelocytes, or marrow cells.

The _red marrow_ is found throughout the femur and the proximal portion of the tibia, and in a few of the pelvic bones and vertebræ in the adult fowl, and in certain other bones of the baby chick. Red marrow consists of a delicate network of connective tissue supporting a dense capillary plexus, a small amount of fat, and numerous cells. The cellular elements of red marrow consist of marrow cells which contain large nuclei and possess ameboid movement, red blood cells, giant cells containing one or more nuclei, and various kinds of leucocytes, including eosinophiles, mast cells, and also osteoclasts.

_Growth of Bone._—In the baby chick, only the shaft and a portion of the extremities of the long bones are thoroughly ossified, the extreme ends, and of the femur most of the articular head, being cartilaginous. The bones grow in length by an increase in the cartilage, the cartilage gradually becoming ossified. Growth in diameter is accomplished by the constant deposition of new layers of bone beneath the periosteum. During this process the osteoclasts absorb the bone from within. The formation of the marrow cavity is thus effected.

=Classification of Bones.=—The bones of the fowl are classified as long, short, flat, and irregular.

_Long Bones._—The long bones occur in the legs and wings, where they serve as levers to sustain weight and make locomotion possible. A long bone consists of a shaft and two extremities. The superior is called the _proximal_ and the inferior the _distal extremity_. The expanded articular surfaces in forming joints with adjoining bones afford ample space for the attachment of ligaments. The shaft is cylindrical and hollow.

_Short Bones._—Short bones occur in the feet and in the wings. Their structure is similar to that of the long bones.

_Flat Bones._—The flat bones occur where extensive protection is needed, as in the cranial region; or where large surface for muscular attachments is needed, as in the costal and pelvic regions. Flat bones are made up of two thin layers of compact bone with a variable amount of cancellous tissue interposed.

_Irregular Bones._—The irregular bones include the vertebræ, the patellæ, and the carpal bones.

=Composition of Bone.=—Bone consists of organic and inorganic matter. Organic matter gives toughness and elasticity to the bone, and inorganic matter hardness. The organic substance of bone is called ossein. When boiled in water ossein is resolved into gelatin. The following tables[1] give the results of an analysis of the femur, fresh, of a mature hen.

Footnote 1:

Grateful acknowledgment is hereby made to Dan M. McCarty, Chemist, Animal Industry Division, North Carolina Agricultural Experiment Station, for this analysis.

Fresh femur: Water 18.23 per cent. Dry matter 81.77 per cent. Dry matter: Organic matter 63.09 parts Inorganic matter 18.68 parts Salts in dry matter: Calcium 6.970 per cent. Magnesium 0.283 per cent. Potassium 0.004 per cent. Sodium 0.276 per cent. Iron 0.020 per cent. Phosphorus 3.210 per cent. Sulphur 0.085 per cent. Chlorine 0.520 per cent. Carbon dioxid 0.550 per cent.

The inorganic matter of the femur of the hen consists of 18.68 parts or 22.84 per cent. of dry matter, and the organic matter of 77.16 per cent. Stated in other words the femur, including its contained marrow, consists of organic and inorganic matter in the ratio of 3.4, approximately, to 1.

=The Skeleton of the Fowl.=—The skeleton of a bird is remarkable for the rapidity of its ossification. It is worthy of note that other parts of the bodies of adult birds also become ossified. Among such parts are the tendons of the muscles of the legs, of the feet, and of the neck; the plates of the corneal margin of the sclerotic tunic of the eye; and the stapes of the ear. Ossification in birds at the attachments of the semi-lunar valves of the aorta and of the pulmonary artery has been reported by Owen.

The bony structure is compact, and the bones contain a greater proportion of phosphate of lime than do the osseous structures of mammals. Especially is this the case in those parts of the skeleton which are permeated by air.

The Divisions Of The Skeleton

( The Skull ( Cranium ( ( Face The Axial skeleton ( ( Cervical region ( ( Dorsal region ( Ribs ( The Vertebral column ( ( Sternum ( Lumbar region ( Sacral region ( Coccygeal region

( Scapula ( Shoulder girdle ( Coracoid ( ( Clavicle ( ( ( Arm ( Humerus ( ( ( Fore limb ( Forearm ( Radius ( ( ( Ulna ( ( ( ( ( Carpus The Appendicular skeleton ( ( Hand ( Metacarpus ( ( Phalanges ( ( Pelvic girdle ( Ilium ( (Hip bone) ( Ischium ( ( Pubis ( ( ( Thigh ( Femur ( Hind limb ( ( Leg ( Tibia ( ( Fibula ( ( Foot ( Metatarsus ( Phalanges

The bodies of birds contain many air reservoirs to make them light that flying may be more easy. Many bones have their weight in proportion to size and strength thus greatly reduced. In very young birds the cavities of bones contain, instead of air spaces, loosely arranged red marrow, which is in most bones later absorbed. The air reservoirs in bones are most capacious in the best flyers. In the non-flyers more of the bones retain their red marrow.

The bones supplied with air spaces are relatively larger than in mammals, and are provided with small transverse osseous columns which cross in different directions and from side to side. These cross beams give stability to the thin wall of the bone. The membranes lining these cavities are very vascular.

The Axial Skeleton

The Skull

The skull is divided into the cranial and facial portions. In these parts we find present 31 bones: one occipital, two parietal, two frontal, one ethmoid, one sphenoid, and two temporal; all of which constitute the cranial group; two premaxillary, two maxillæ, two nasal, two lacrimal, two palatine, two pterygoid, two zygomatic, one vomeral, the two jugal, and two quadrato-jugal, which constitute the facial group; two quadrati and one inferior maxillary, which constitute the inferior jaw group.

The peculiarities of the skull are the long os incisivum and the single condyle located on the occipital bone just below the foramen magnum. The condyle articulates with the atlas.

The head of the bird is small in proportion to the size of the body, and in front it is conical in shape.

The Cranium

The cranial cavity, or cavum cranii, incloses the brain with its membranes and vessels.

The dorsal wall, or roof, is formed by the frontal and the parietal bones. In the median line of the cerebral portion is the internal parietal crest. The roof of the cerebellar portion is marked centrally by a groove.

The posterior wall of the cerebellum is formed by the occipital bone.

The lateral wall is formed chiefly by the temporal bone. It is marked by a ridge which divides the cavity into the cerebral and cerebellar compartments. The cerebral portion is marked by a depression which receives the optic lobes. A crest divides this cavity from the optic portion. The walls are marked by digitations and vascular grooves.

[Illustration:

FIG. 4.—The skeleton of the domestic fowl. 1, Os incisivum. 2, External nasal opening. 3, Os nasale. 4, Os lachrymale. 5, Lamina perpendicularis. 6, Os dentale. 7, Os palatine. 8, Os quadrato-jugal. 9. Os pterygoideum. 10, Os quadratum. 11, Os articulare. 12, External auditory canal. 13, Atlas. 14, Os carpi radiale. 15, Radius. 16, First finger. 17, Os metacarpus. 18, Second finger. 19, Third finger. 20, Os carpi ulnare. 21, Ulna. 22, Humerus. 23, Thoracic vertebræ. 24, Scapula. 25, Os ilium. 26, Foramen ischiadicum. 27, Caudal vertebræ. 28, Pygostyle. 29, Foramen obturatum. 30, Os ischium. 31, Processus uncinatus. 32, Vertebral rib. 33, Os claviculum or furculum. 34, Os coracoideum. 35, Os femoris. 36, Os pubis. 37, Body of sternum. 38, Lateral internal process of sternum. 39, Costal process of sternum. 40, Sternal crest, cristi sterni, or keel of breast-bone. 41, Sternal rib. 42, Lateral external process of sternum. 43, Os fibula. 44, Xyphoid process of sternum. 45, Internal notch. 46, Os patella. 47, Os tibia. 48, Os metatarsus. 49, Second toe. 50, Fourth toe. 51, Os metatarsale. 52, First toe. 53, Second toe. 54, Second phalanx of second finger. 55, Os metacarpus. 56, Air opening in humerus. 57, Hypocledium. 58, External notch. 59, Cervical vertebræ. 60, Foramen oblongum. ]

The ventral wall, floor, or basis cranii interna, may be regarded as forming five fossæ. These are: one anterior, one middle, one posterior, and two lateral. The _anterior fossa_ supports the frontal and olfactory parts of the cerebrum. It lies at a higher level than the middle fossa. The _middle fossa_, or _fossa cranii media_, is circular in outline and extends into the lateral fossæ which lodge the olfactory lobes. Just back of the middle fossa is the sulla turcica, upon which rests the pituitary body. The _posterior fossa_, or _fossa cranii posterior_, lodges the medulla oblongata.

=Bones of the Cranium= (Figs. 4, 6, 7, and 8).—The bones of the cranium fuse early in the chick’s life. The sutures uniting the bones can usually be seen in the fetus or in the baby chick soon after it emerges from the shell. The major portion of the cranial bones become entirely fused. Each cranial and each facial bone ossifies from a distinct center or centers.

The cavity for the cerebrum is much larger than the cavity for the cerebellum. The cranial cavities in birds are relatively larger than in mammals. The bones are designated as in mammals. There are three single bones, the occipital, the ethmoid, and the sphenoid. Those in pairs are the frontal, the parietal, and the temporal.

=The Occipital.= _Location._—The occipital bone or os occipitale, is situated at the posterior part of the cranium, of which it forms the posterior wall. This part is called the base of the cranium. The occipital bone articulates with or touches inferiorly, the sphenoid, laterally, the temporal, and superiorly, the parietal.

_Development._—The occipital bone is developed from four centers of ossification; the dorsal, or os occipitale superius, two lateral, or ossa occipitales laterales, and the ventral, or os occipitale inferius, all of which may be seen distinct in the baby chick (Fig. 5, Part II, No. 1).

[Illustration:

FIG. 5.—Bones of the head and vertebra.

Part I.—1, The cranium. 2, The skull cap. 3, The ethmoid bone. 4, The inferior maxilla. 5, The palatine bone. 6, The quadrato-jugal. 7, The jugal. 8, The superior maxilla. 9, The premaxilla. 10, The horny covering for the premaxilla. 11, The horny covering for the os dentale. 12, The os quadratum. 13, The nasal bone. 14, The pterygoid.

Part II.—1, The os occipitale (1, dorsal; 2, two lateral; 3, ventral portions and 4, foramen magnum). 2, The fourteen cervical vertebræ. (1, atlas; 2, axis). 3, The seven dorsal vertebræ. 4, The fourteen lumbo-sacral vertebræ. 5, The seven coccygeal vertebræ. 6, The pelvis (1, ilium; 2, ischium; 3, pubis; 4, cotyloid cavity or acetabulum). 7, The vertebral column complete from the baby chick. 8, The parietal bone. 9, The temporal bone. 10, The frontal bone. ]

_Description._—In the center of the occipital bone is the _foramen magnum_. Through this foramen the spinal cord extends into the cranial cavity and connects with the medulla oblongata. The occipital bone has a single condyle, which is located just below the foramen magnum and articulates with the atlas. At the base of the condyle a small _subcondyloid fossa_ receives the body of the atlas during extreme flexion of the head. In the center of the lateral wing of the occipital bone there is a small foramen through which passes the hypoglossal nerve. Somewhat laterally from this foramen there is an opening through which the vagus, or pneumogastric nerve passes. Laterally from these is the _canalis caroticus et jugularis_. Between the os occipitale superius, or dorsal portion, and the ossa parietalia is a space to which ligaments are attached, called the fontanel.

[Illustration:

FIG. 6.—View of the frontal region of the skull of a hen. 1, Parietal. 2, Frontal. 3, Nasal. 4, Premaxilla. 5, Temporal. 6, Inferior jaw. 7, Jugal bone. ]

=The Ethmoid.= _Location._—The ethmoid, or os ethmoidale, forms the anterior wall of the cranium, and the orbital septum. It is related anteriorly with the vomeral, superiorly with the nasal and frontal, posteriorly with the temporal, and inferiorly with the sphenoid, and palatine.

_Description._—The ethmoid consists of a perpendicular and a horizontal lamina. The perpendicular lamina, located between the orbital cavities, is called the _septum interorbitale_. On each side of the septum interorbitale and near the superior orbital roof are two foramina for the passage of the olfactory nerves. In the horizontal plate, which forms the anterior cranial wall, are located the _optic foramina_ through which pass the optic nerves.

[Illustration:

FIG. 7.—Side view of the skull of a hen. 1, Lamina perpendicularis. 2, Foramen for the passage of the nerve of smell. 3, Foramen for the passage of the optic nerve. 4, Nasal bone. 5, External nasal opening. 6, Premaxilla. 7, Os dentale. 8, Superior maxilla. 9, Os jugal. 10, Os quadrato-jugal. 11, Os quadratus. 12, Pterygoideus. 13, Os articulare. 14, Inferior maxilla. 15, Temporal. 16, External auditory canal. 17, Parietal. 18, Frontal. 19, Palatine. 20, Orbital process, posterior to which is the processus zygomaticus. 21, Interorbital foramen and optic foramen for passage of optic nerve. 22, Attachment for inferior oblique; 23, for superior oblique; 24, for levator palpebræ superioris; 25, for internal rectus; 26, for superior rectus; 27, for external rectus; 28, for inferior rectus; 28, for inferior rectus; 29, for depressor palpebræ inferioris; 30, for orbicularis palpebrarum; 31, for tensor tympani; 32, for circumconcha. ]

=The Sphenoid.= _Location._—The sphenoid, or os sphenoidale, forms the floor of the cranial cavity and articulates with or touches posteriorly the occipital, laterally the temporal, and anteriorly the palatine, and ethmoid.

_Description._—The sphenoid bone, the largest part of the cranial floor, is formed by the fusion of the nasal and the cranial parts. It is a three-cornered bone with two, thin, broad wings. These wings are divided into two portions, orbital wings, or _alæ orbitales_, and temporal wings, or _alæ temporales_. The temporal wing forms a cover for the Eustachian tube trumpet, and for the canal coming from the sella turcica, which latter gives passage to the intracranial carotid artery. The orbital wing forms the lower portion of the posterior wall of the orbital cavity, and lies directly before the os petrosum or temporal bone where the second and third branches of the fifth pair of cranial nerves emerge from the cranial cavity.

Anteriorly the sphenoid has a foramen for the passage of the Eustachian tube, the _tuba auditiva_, and also a sharp-pointed projection, the nasal portion, called the _rostrum_.

=The Frontal.= _Location._—The frontal bones, or ossa frontales, two in number, form the forehead, a portion of the nose, and a portion of the roof of the orbital cavities. They are related posteriorly with the parietal, laterally with the temporal and zygomatic, and anteriorly with the nasal and premaxillary. They touch inferiorly the ethmoid.

_Description._—Each of these bones has a _processus orbitalis_ which is seen at the outer margin of the posterior and upper orbital wall and just in front of the zygomatic process of the squamous portion of the temporal. The frontal bone forms the anterior portion of the superior wall of the cranial cavity. The two bones are thin, flat, and meet at the median line of the forehead. The external surface is convex. The inner surface has a ridge located longitudinally and in the center the bone becomes narrow anteriorly.

=The Parietal.= _Location._—The parietal bones, or ossa parietalia, two in number, form the posterior part of the roof of the cranial cavity. They meet in the median line and are related posteriorly with the occipital, anteriorly with the frontal, and laterally with the temporal bones.

_Description._—The parietal bones are short and very broad (Fig. 5, Part II, No. 8). Each bone is quadrilateral in outline and has two surfaces, four borders and four angles. The external parietal surface is convex and smooth and the internal, cerebral surface is concave.

=The Temporal.= _Location._—The temporal bones, or ossa temporales, two in number, are located at the lateral portion of the cranium, and aid in the formation of the cranial wall. The temporal bone is related posteriorly with the occipital, superiorly with the parietal and frontal, externally with the quadratus, anteriorly with the ethmoid, and inferiorly with the sphenoid.

_Description._—The temporal bones consist of the fused squamous and petrous temporals; they contain the essential organs of hearing.

[Illustration:

FIG. 8.—Inferior view of the skull of a hen. 1, Occipital. 2, Foramen magnum. 3, Occipital condyle and just below the basi-occipital. 4, Foramen for the passage of the hypoglossal nerve. 5, Foramen for the passage of the vagus. 6, Canalis caroticus and jugulare. 7, Sphenoid. 8, Temporal wings of the sphenoid. 9, Foramen auditiva. 10, Os articulare. 11, Os angulare. 12, Vomer. 13, Os dentale. 14, Pterygoid. ]

The _squamous portion_ of the temporal bone possesses the long thin zygomatic process sometimes called the _posterior orbitalis_. It forms a small flattened tongue, directed forward, sometimes free, and at other times united by its superior border to the summit of the orbital process. This is especially true in the turkey. This process is seen near the lower outer portion of the posterior orbital wall. The squamous portion is also provided antero-laterally with an articular facet which articulates with the quadrate bone. The large portion of the temporal bone lies on the side of the cranium superior to the ala sphenoida temporale. It extends outward and anteriorly over the rims of the petrosum and ala sphenoida orbitale. The squamous part forms the upper three-fourths of the cochlea, the inner auditory canal, the upper part of the fenestra ovalis, the anterior vertical and the outer semicircular canal, and the lower part of the posterior vertical semicircular canal.

The _petrous portion_ forms the posterior wall of the foramen ovale and the fenestra ovalis in which lies the columella. The fenestra ovalis and the fenestra rotunda are the only two entrances into the labyrinth. In this region may be seen the fusion line between the os petrosum and the os occipitale. Superiorly and posteriorly the petrous portion touches the external parietalia and occipitalis; infero-laterally it unites with the basi-sphenoid. The outer rim of the foramen ovale is broadened by the ala sphenoida and mesially by the basi-sphenoid. This foramen gives exit to the second and third divisions of the fifth pair of cranial nerves.

The lateral surface of the temporal bone presents a short tube, the _external acoustic process_, or _processus acusticus externus_, to which is attached the concha of the ear. The process is directed outward. Its lumen, the _external acoustic meatus_, or _meatus acusticus externus_, conducts to the cavity of the middle ear in the bare skull, but is separated from it by the tympanic membrane in the natural state.

Bones Of The Face

The bones of the face, or ossa faciei, are the premaxillary, or upper mandible, the maxillæ, the nasal, the lacrimal, the palatine, the pterygoid, the zygomatic, the vomeral, the jugal and the quadrato-jugal. The vomer is single, the others are paired. In the inferior maxillary group there are the quadrati, and the inferior maxillary, or lower mandible. The turbinated and hyoid bones are also discussed with the bones of the face.

The beak consists of the anterior portion of the upper and lower mandibles which are covered with a horny structure.

=The Premaxilla.= _Location._—The premaxillæ, or ossa incisiva, or mandibular structures, are located in the extreme anterior facial region.

_Description._—The premaxillæ are long and the anterior end is pointed. Each consist of two lateral halves which become fused before the chick is hatched. They partly circumscribe the openings into the nose. This bone is the base of the upper portion of the beak and determines its form. It forms the anterior walls of the nasal cavity. It has between the nasal bones, two processes which extend back to the anterior point of the cerebral cavity. The posterior part of the incisivum and nasale are flat, thin, and elastic. The extensions then are the _processus maxillaris_, the _processus palatinus_, and the _processus frontalis_, the first of which forms part of the jaw rim, the second, which aids in forming the gum plate, and the last which reaches to the anterior portion of the cranial wall.

=The Maxilla.= _Location._—The superior maxillaries, or ossa maxillares, two in number, form the floor of the upper beak, a part of the palatine roof and nasal walls.

Each maxilla borders laterally the premaxilla and the nasal; inferiorly, the anterior point of the palatine; and posteriorly, the jugale.

_Description._—The maxillæ are thin, flat, bones. They have three borders and three angles. The palatine processes of the two bones do not meet in the median line, which results in a cleft in the median palatine region. The bone-like gums are formed partly by the palatine processes but more largely by lateral wings of the os incisivum. Each maxilla has posteriorly a yoke-like extension, superiorly a small extension, and also a palatine process. The latter articulates by a facet with the vomer.

=The Nasal.= _Location._—The nasal bones, or ossa nasalia, two in number, are located in the lateral facial region. The nasal bone articulates posteriorly with the frontal; laterally, on the inner border, with the processus frontalis of the premaxilla, and on the outer border with the lacrimal; and inferiorly with the premaxilla, maxilla, jugale, and vomer.

_Description._—The nasal bone, or os nasale, is broad, flat, and elastic and forms the posterior wall of the nasal opening. Under this bone is located the infraorbital sinus.

There are three extensions: first, the _processus intermaxillaris_, which forms the upper wall of the nasal cavity; second, the _processus maxillaris anterior_, directed downward and forward, which fuses with the maxillary bone and forms the posterior rim of the nasal cavity; and third, a _posterior processus frontalis_, which lies parallel with the ethmoid.

=The Lacrimal.= _Location._—The lacrimal bones, or ossa lacrimalia, two in number, are located at the outer border and at the junction of the processus frontalis of the nasal, with the frontal bone.

_Description._—The lacrimal bone is small, and rather filiform. They become fused with the nasal and the frontal bones, forming part of the margin of each.

=The Palatine.=—_Location._ The palatine bones, or ossa palatina, two in number, enter into the formation of the inner part of the bony gum and hard palate, or roof of the mouth. They form the support for the hard palate. Each palatine articulates posteriorly with the rostrum, or nasal portion of the sphenoid, and with the pterygoid; and anteriorly with the maxilla.

_Description._—The palatine bone is curled posteriorly and is thin at the upper portion and thick at the lower border. Anteriorly it has a long rather filiform projection.

=The Pterygoid.= _Location._—The pterygoid bones, or ossa pterygoidea, two in number, are located back of the region of the posterior nares. They extend diagonally outward and backward from the median region of the sphenoid rostrum to the quadrate bone. They articulate anteriorly with the sphenoid rostrum and the palatine, and posteriorly with the quadrate.

_Description._—The pterygoid bones are slender and cylindrical, and are expanded at the ends into an articular facet.

=The Zygomatic.= _Location._—The zygomatic, or ossa zygomatica, two in number are situated below the orbital cavity and extend from the maxilla to the quadrate bone.

_Description._—The zygomatic is small, slender, rod-shaped, and forms the lateral portion of the upper jaw. The anterior portion of the zygomatic represents the jugal and is fused with the maxilla and with the anterior processus maxillaris of the nasal bone, the maxilla, and the posterior portion, the quadrato-jugal, which articulates with the quadrate bone.

=The Vomer.= _Location._—The vomer is located in the median nasal septum. It articulates with the rostrum of the sphenoid, being connected to it by a mass of ligaments. It touches anteriorly the posterior portion of the maxilla.

_Description._—The vomer is a median bone and aids in the formation of the septum nasi. It consists of a thin plate, thickest posteriorly and diminishing toward the anterior edge.

=The Jugal and Quadrato-jugal.=—The jugal and quadrato-jugal are united forming a long slender cylindrical bone called the zygomatic, lying at the outer side of the upper jaw. They have been described under zygomatic, which see.

=The Quadrate.= _Location._—The quadrate bones, or ossa quadrata, two in number, are located antero-laterally to the temporal bones. Each articulates inferiorly with the posterior articular portion, or pars articulare, of the inferior maxilla and infero-laterally with the quadrato-jugalare portion of the zygomatic. It articulates antero-internally with the pterygoid and supero-posteriorly with the temporal.

_Description._—The quadrate bone is anvil-like in shape. It has an anterior process, the orbital process, for muscular attachments, and posteriorly it affords attachment to the ear drum.

=The Inferior Maxilla.= _Location._—The inferior maxilla, lower jaw, or os maxillare inferius, also called the mandibular bone, or pars dentis, is analogous to the lower jaw of mammals. It articulates posteriorly with the quadrate bone.

_Description._—The inferior maxilla is the largest bone of the face. It is made up of a _right_ and a _left limb_ which are separate in the fetus and which unite subsequently anteriorly, forming the inferior portion of the beak. Each limb of the jaw is developed from five elements: the _pars articularis_, which forms the jaw-joint and, expanded, articulates with the quadrate bone; the _pars angularis_, lying just in front of the pars articularis; the _pars supra-angularis_, a slender bone lying just above the angularis; the _splenial_, a thin plate of bone, lying along the inner surface of the mandible; and the _pars dentalis_, which forms the anterior portion of the jaw.

=The Turbinate Bones.= _Location._—The turbinate bones, or ossa turbinata, six in number, are attached to the lateral walls of the nasal cavity (Fig. 26, No. A, 1 and 2). In each nasal cavity there are three turbinate bones, one anterior and two posterior. Of the two posterior the upper one lies supero-posterior to the inferior one. The turbinate bones are attached to the lateral nasal walls, project into the cavity and thus greatly diminishing its extent.

_Description._—Each turbinate bone is composed of a very thin lamina, finely cribriform in many places, and in the fresh state, covered on both sides with mucous membrane. These bones are curled and partly membrano-cartilaginous structures which give greater surface in the nasal passage for mucous membrane in which the olfactory nerve terminal filaments are distributed.

=The Nasal Cavity.=—The nasal cavity, or cavum nasi, is a longitudinal passage which extends through the upper part of the face. It is divided into right and left halves by a median septum nasi. Its walls are made up of the premaxilla, maxilla, nasal, vomer, and palatine bones.

=The Hyoid Bone.= _Location._—The hyoid bone, or os hyoideum, is situated chiefly between the rami of the mandible, but its upper part extends around the outer margin of the base of the skull. The hyoid bone does not articulate with any bones of the skull, but is firmly attached by strong fibrous structure.

_Description._—The hyoid bone consists of the following parts: the _body_, or _basi-hyal_, which is subcylindrical and presents in front a trochlear articular surface, convex transversely, and concave vertically for articulation with the ewer-shaped portion of the glosso-hyal. The anterior free portion, or lingual process, is called the _glosso-hyal_, or _entoglossal bone_. The lingual process gives support to the muscular and fibrous structures of the tongue. On either side of the basi-hyal there is a limb passing posteriorly along the side of the superior larynx, extending upward along the outer border of the occipital bone. This is the _cornu_ of the os hyoideum and is divided into two elements, first, the _basi-branchial_ which is bone and articulates with the basi-hyal, and the second, the _cerato-branchial_, cartilaginous in structure. In the center and projecting backward from the body of the os hyoideum is a spur process called the _uro-hyal_, partly bony and partly cartilaginous, and which rests upon the superior larynx.

The Vertebral Column

The vertebral, or spinal column consists of 42 bones, as shown in the following table:

Cervical region 14 Dorsal region 7 Lumbo-sacral region 14 Coccygeal region 7 —— Total 42

Many of the bones of the dorsal and lumbo-sacral regions do not have free articulations. The cervical and coccygeal alone have free movements.

=The Cervical Vertebræ= (Fig. 4, No. 59; Fig. 5, Part II, No. 2). _Location._—The cervical vertebræ form the neck of the fowl.

[Illustration:

FIG. 9.—Os hyoidum and tongue muscles. 1, Glosso-hyal. 3, Basi-hyal. 4, Basi-branchial element of the cornua. 5, Cerato-branchial element of the cornua. 6, Uro-hyal or spur process. 7, Genio-hyoideus. 8, Cerato-hyoideus showing the slender tendon. 9, Hyoideus transversus. 10, Hyoideus transversus. ]

_Description._—The long cervical section of the spinal column is S-shaped and is made up of fourteen vertebræ. The anterior segments move freely forward, the middle ones backward and the posterior ones forward, allowing the S-shaped curve of the neck. The neck is flexible so that it is possible for the beak to reach the coccygeal oil gland. The bird is enabled to reach the feathers on all parts of the body to cleanse and oil them.

=The Atlas.= _Location._—The first cervical vertebra is called the atlas. Anteriorly it articulates with the single condyle of the occipital bone. Posteriorly it articulates with the axis, or second cervical vertebra.

_Description._—The atlas is the smallest of the cervical vertebræ and is ring-shaped. The anterior articular surface, half-moon in shape, forms a deep articular cavity. The joint, called a ball-and-socket joint, makes possible movements in all directions. The condyle of the occiput also touches an articular end of the odontoid process of the axis, or second cervical vertebra. Posteriorly there projects from the atlas two small lateral wings possessing articular facets which articulate with similar facets on the lateral wings of the axis. Posteriorly the body of the atlas is also provided with an articular surface which articulates with a similar surface on the anterior portion of the body of the axis.

=The Axis.= _Location._—The axis is the second cervical vertebra. It articulates anteriorly with the atlas, and by a facet on the extreme anterior end of the odontoid process, with the condyle of the occipital bone. Posteriorly it articulates with the third cervical vertebra.

_Description._—The body of the axis is short. The upper anterior portion of the body of the axis is provided with a tooth-like process called the _odontoid process_. There are two anterior lateral wings provided with small articular facets which articulate with similar facets of the atlas. The anterior surface of the body of the axis forms a true articulation with the body of the atlas.

The axis is provided with a _superior_ and an _inferior spine_. There are two posterior articular processes which articulate with the prezygapophyses, or anterior articular processes, of the third cervical vertebra. The posterior part of the body of the axis forms a true articulation with the body of the third cervical vertebra.

=Other Cervical Vertebræ.=—Beginning with the axis, the body of which is relatively short, the body of each succeeding vertebra is longer than that of the preceding. The articulations of each vertebra with adjoining vertebræ are effected by means of diarthrodial facets, convex in one direction and concave in the other.

[Illustration:

FIG. 10.—_A._ Diagram of three first dorsal vertebræ and scapular arch-side view. _B._ Diagram of section through the hemal arch.

_A._ 1, First dorsal segment. 2, Second. 3, Third. 4 and 5, Hemal arches. 6, The pleurapophyses or floating ribs. 7, The third pleurapophyses or dorsal vertebral rib articulating with the hemapophysis or sternal rib, 8, and this in turn with the wing of the sternum form a hemal arch. 9, The sternum. 10, Intervertebral foramen through which the nerves pass. 11, Articulation with the body of vertebra parapophyses. 12, Articulation with transverse process or diapophyses. 13, Oblique process or zygapophysis. 14, The epipleural appendage.

_B._ 1, Hemal or inferior spine (hypapophysis). 2, The neural arch. 3, The pleurapophyses or rib. 4, The superior or neural spine or neurapophysis which aids in the formation of the anapophyseal ridge. 5, Parapophyseal surface for head of rib. 6, Tubercle of rib articulating with the diapophysis. 7, Lamina of neurapophysis. 8, Centrum. 9, Hemal arch. ]

Between the bodies of the vertebræ are pads of fibrous cartilage. Above these bodies and inferior to the neural spines extends throughout the spinal column the large _neural canal_ which is occupied by the spinal cord. Between the vertebral segments the neural canal is exposed superiorly, since here the neural arches do not completely bridge the canal. These spaces are protected by intervertebral ligaments.

In addition to the superior neural spines and the inferior spines, from the body of the vertebra project _lateral processes_, and anterior and posterior _oblique processes_.

All cervical vertebræ except the atlas and the axis are made up of the following parts: a body, or centrum, a neural canal, a neural arch, a superior dorsal, or neural spine, or neurapophysis, which in most cervical vertebræ is only slightly developed, two oblique processes, or zygapophyses, two transverse processes, or diapophyses (Fig. 10, No. 12) and in some vertebræ two tubercles, or anapophyses above the posterior zygapophyses. The _prezygapophyses_ are directed upward and inward; the _postzygapophyses_ are directed downward and outward. The inferior spines are only well developed in the last two or three cervical vertebræ.

Between vertebral segments, except the central sacral portion, on each side, there is an _intervertebral foramen_ (Fig. 11, No. _A_, 4), through which pass the spinal nerves. In the central portion of the sacrum where the vertebræ have fused, there are two foramina on each side for each original vertebra, one located above the other, the upper giving passage to the sensory branch, the lower to the motor branch of the nerve.

=The Dorsal Vertebræ= (Fig. 4, No. 23; Fig. 11, _A_). _Location._—The dorsal, or thoracic vertebræ, or vertebræ thoracicales, aid in forming the roof of the chest cavity.

_Description._—The dorsal vertebral section is made up of seven vertebræ, with strong short bodies. The first and sixth dorsal segments articulate as do the cervical, by the bodies and oblique processes. (Fig. 11, No. _A_, 3, illustrates the oblique processes.) The seventh dorsal is fused with the first lumbo-sacral vertebra. The second to the fifth inclusive of the vertebræ are fused together, and the superior and inferior spinous processes are fused into a prominent plate-like ridge.

The transverse processes of the dorsal vertebræ, from the second to the sixth, are well developed and are bridged over with a thin layer of bone. The ventral spines are partly fused and form a very prominent and continuous ridge. (Fig. 11, No. _A_, 1, shows the fused superior spines; No. 2, the fused inferior spines; and No. 4, the intervertebral foramina.)

=The Lumbo-sacral Vertebræ= (Fig. 5, Part II, No. 4). _Location._—The fused lumbo-sacral section of the spinal column forms the roof of the pelvic cavity.

[Illustration:

FIG. 11.—Bones from the scapular arch.

_A._ Dorsal vertebra. 1, Superior spinous ridge, 2, Inferior spinous ridge. 3, Oblique processes. 4, Intervertebral foramina. 5, Articular facette for head of the rib. 6, Articular facette for tubercle of the rib. 7, Articular portion of the body.

_B._ Outer surface of scapula.

_C._ Inner surface of scapula. 1, Thin caudal end. 2, Articular head. 4, Processus furcularis. 5, Processus humeralis. 6, Processus coracoideus.

_D._ Outer surface of coracoid.

_E._ Inner surface of coracoid. 1, The furcular tuberosity. 2, Articular facette for articulation with the sternum. 3, Articular surface for humerus and scapula.

_F._ Outer surface of humerus and G the inner surface of the same. 1, Trochanteric fossa. 2, Oval articular head at proximal end. 3, Shaft. 4, Distal end showing articular condyles. 5, Trochanter. 6, Trochlea for ulna. 7, Trochlea for radius. 8, Depression or fossa.

_H._ Section through the median plane of the humerus showing the delicate cross partitions illustrating provisions made for bones provided with air-sac extensions. ]

_Description._—The lumbo-sacral region consists of fourteen vertebræ which are distinct in the body of the newly hatched chick, but which become fused soon after hatching. With these vertebral segments there are fused the last dorsal and first coccygeal vertebral segments. This fusion is so complete that the segments are indicated only by the intervertebral foramina on the sides through which the spinal nerves pass, and by transverse markings on the inferior surface of the bodies.

The lumbo-sacral vertebræ, called the sacrum, and the ilia are fused. The dorsal spines of the vertebral segments are indicated only in the anterior portion where they are fused, forming a plate. There are no prominent ventral spines.

=The Coccygeal Vertebræ= (Fig. 4, No. 27). _Location._—The coccygeal or caudal vertebræ, or vertebræ coccygeæ, constitute the bones of the tail.

_Description._—There are seven coccygeal vertebræ. The last segment, shaped like a plough share and therefore called the pygostyle, is the largest and is supposed to have been formed by the fusion of several original distinct segments. It supports the coccygeal oil gland and the row of rudder feathers, or rectrices, which are arranged fan-wise.

All of the coccygeal vertebræ except the first are freely movable, thus allowing the tail to be used as a rudder during flight. The lateral spines are long and well developed, and the superior spines are bifurcated, thus giving increased surface for muscular attachment. The first coccygeal segment is fused with the last lumbo-sacral vertebra.

The Thorax

The dorsal vertebræ superiorly, the ribs laterally, and the sternum, or breast-bone inferiorly, form the skeleton of a large cavity called the thorax. The dorsal vertebræ have been described.

=The Ribs= (Fig. 4, No. 32; Fig. 10, _A_ and _B_). _Location._—The ribs form the lateral bony wall of the thorax, articulating superiorly with the dorsal vertebræ.

_Description._—The ribs are arranged in order of length, the ultimate rib being the longest. From anterior to posterior, they approach more nearly a horizontal position. The ribs are divided into the true and the false. The _true ribs_ articulate with the sternum. The _false ribs_ do not touch the sternum; they are floating. The true ribs are composed of two parts, a vertebral, or dorsal, and a sternal, or ventral. The vertebral part, or _extremitas vertebralis_, is provided with an articular head, or _caput costæ_; a neck, or _collum costæ_; and an articular tubercle, or _tuberculum costæ_. The head and tubercle articulate with the dorsal vertebra. Below the head of each rib is a _pneumatic foramen_.

The distal extremity of the dorsal section of the rib articulates with the proximal end of the sternal section by a diarthrodial articulation.

The articulations of the true ribs with the sternum is diarthrodial and each articulate by two small ridges with a double sternal facet. The first, the second, and the seventh ribs are floating, or false ribs. The first rib articulates with the quadrate part of the last cervical vertebra and also with the first dorsal vertebra. The seventh, the last rib, articulates with the under side of the anterior alar part of the ilium. This rib is situated similarly to the true ribs; but, instead of articulating directly with the sternum, the lower end lies against the sternal segment of the rib just anterior to it.

From the posterior edge of the second, the third, the fourth, and the fifth ribs, and near the middle of the dorsal segment, are flat, uncinate, bony processes which project upward and backward, overlying in each case, the succeeding rib and giving greater surface for muscular attachments and greater stability to the thorax.

=The Sternum= (Fig. 4, No. 40; Fig. 10, No. _A_, 9). _Location._—The sternum, or breast-bone forms the inferior portion, or floor of the thoracic cavity.

_Description._—The sternum is a quadrilateral, curved plate with processes projecting from each angle and from the middle of the anterior and posterior borders. The posterior medial projection, or _metasternum_, is the longest, and has a tall, plate-like ridge—the _sternal crest_, _crista sterni_—running along its ventral surface. The crest serves the important function of increasing the bony area for the attachment of the powerful muscles which move the wings. The anterior medial projection, or _rostrum_, is short, and pierced at its root by an opening from which extend two elongated, saddle-shaped depressions into which the end of the coracoid bones are received.

The plate-like process of bone, the _posterior lateral process_, which projects from the caudal angles of the sternum soon divides into two parts. The shorter of these, the _oblique process_, broadens toward its free end and covers the sternal segments of the last two ribs. The sides of the sternum are thus provided with an external and an internal process forming an _external_ and an _internal_ notch. These notches are bridged over by a broad ligament, to which the muscles are attached. In poor flyers, as the domestic fowl, these notches are large. The posterior end of the sternum is called the _xiphoid process_ or _processus xiphoideus_. Anteriorly the sternum is provided with lateral external processes, the _costal processes_. The lateral borders of the sternum are pitted by four depressions into which the sternal segments of the ribs are received. The dorsal, or inner surface of the bone is pierced by openings by which the air-sacs communicate with the interior.

The Appendicular Skeleton

The appendicular skeleton consists of the shoulder girdle, the fore limb, the pelvic girdle, or hip bone, and the hind limb. The shoulder girdle consists of the scapula, the coracoid, and the clavicle. The fore limb consists of the arm, forearm, and the hand. The arm consists of the humerus, the forearm of the radius and the ulna; and the hand consists of the carpus, the metacarpus, and the phalanges. The pelvic girdle consists of the ilium, the ischium, and the pubis. The hind limb consists of the thigh, the leg, and the foot. The thigh consists of the femur, and the leg consists of the tibia and the fibula. The foot consists of the metatarsus and the phalanges.

The Shoulder Girdle

The shoulder girdle consists of the scapula, the clavicle and the coracoid.

=The Scapula.= _Location._—The scapula (Fig. 11, _A_, _B_) lies on the outer and superior rib surface, extending parallel with the dorsal vertebræ.

_Description._—The scapula is a thin, sword-like bone, becoming thicker as it approaches the shoulder-joint. The scapula expands and becomes thin near the free end, which reaches nearly to the antero-lateral portion of the ilium (Fig. 4, No. 24). The scapula articulates with the coracoid. A _pneumatic foramen_ is located at the base of the acromion process. The anterior part of the scapula is provided with an articular head and is provided with an inner process, called the _processus furcularis_, which lies near the furcula and coracoid. An outer stronger _processus humeralis_ forms the posterior half of the _glenoid cavity_, or _cavitas glenoidalis_, in which the humerus articulates and the processus coracoideus.

=The Clavicle.= _Location._—The clavicles, commonly known as the wish bone, are located in the anterior chest region.

_Description._—The clavicles are long, slender bones uniting below in the _hypocledium_, a laterally flattened process. They are joined to the upper end of the coracoid by fibrous cartilage. The hypocledium is joined to the anterior point of the sternum by the claviculosternal ligament. The clavicles, as united by the hypocledium, form a v-shaped structure called the furculum, or, popularly, the wish bone.

The forks play the part of an elastic spring, whose office it is to prevent the wings from coming toward each other during contraction of the depressor muscles. The conformation of this bone is, therefore, like the sternum, related to the extent and power of flight; and for this reason it is that, in swift flyers, the two branches of the furculum are thick, solid, widely separated, and curved like a U; while in those that fly heavily and with difficulty, these branches are thin and weak, and join at an acute angle. The latter formation greatly diminishes its strength, and lessens, in a singular manner, the reactionary power of the bony arch it represents.

=The Coracoid.= _Location._—The coracoid is located just back of the clavicle and at the side of the entrance of the thoracic cavity. It is the strongest bone of the shoulder girdle, extending upward, outward, and forward. It articulates inferiorly with the sternum and superiorly with the humerus and the scapula, and is attached to the superior end of the furcular limb by a fibrous cartilage.

_Description._—It is thinnest in the center or shaft and broadens toward the inferior extremity. The upper hook-like part of the coracoid forms the fore part of the glenoid cavity, and together with the scapula and furcula form the foramen triosseum through which passes the tendon of the elevator muscle of the wing. The upper end flattens out into three tuberosities, the tuberositas furcularis which is thick and to which attaches the limb of the furcula, the tuberositas scapularis which unites to the scapula, and the tuberositas humeralis which lies between these and articulates with the humerus.

The Fore Limb

The bones of the fore limb are humerus, ulna, radius, carpus, metacarpus, and phalanges.

=The Humerus.= _Location._—The humerus constitutes the arm, which, when at rest, lies parallel to the dorsal vertebræ. It articulates superiorly with the glenoid cavity, a shallow ball-and-socket joint, formed by the scapula and the coracoid; and inferiorly with the ulna and radius.

_Description._—The proximal extremity of the humerus is provided with a trochanter (Fig. 11, _G_, No. 5) and a large oval head or caput humeri, which articulates in the glenoid cavity. The head is an elongate, semi-oval convexity, with the long axis transverse from the radial to the ulnar side and with the ends continued into upper and lower crests. The upper crest of the head of the humerus is on the radial side and the lower crest on the under side. Under this latter crest there is a _pneumatic fossa_ (Fig. 11, _F_, No. 1), at the upper end of which there is an opening into the bone, the _pneumatic foramen_, which brings the air-sac into communication with the air space of the bone. The shaft, or corpus humeris, is irregularly cylindrical and slightly S-shaped.

The proximal part of the shaft, which is expanded on the palmar side, is concave across and convex lengthwise. The distal part is slightly flattened. The shaft of the humerus is almost cylindrical.

The distal extremity of the humerus is provided with two articular condyles, one of which articulates with the ulna and the other with the radius. On the radial side of the palmar surface there is a ridge; and on the ulnar side of the same surface there is a second ridge diverging to the opposite tuberosity. The radial surface is a narrow, subelongate convexity, extending from the middle, approximately, of the palmar surface, obliquely to the lower part of the radial tuberosity. The two _articular convexities_, or _trochlea_, at the distal end of the humerus are bent toward the palmar aspect, the _anconal aspect_ is the side on which the elbow is situated. The inner convexity is the larger and articulates with the ulna. To the outside is the _processus cubitalis humeri_. The outer articulates with the radius and is so arranged that the radius makes a greater flexion than the ulna. At the lower end of the humerus there is a depression which receives the anconeus of the ulna during flexion and extension of the forearm. On the shoulder- and elbow-joint are found grooves over which the tendons glide, at which places sheaths are provided. This arrangement also aids in keeping the capsular ligament in place.

=The Ulna.= _Location._—The ulna, larger than the radius, is bent and articulates with the radius only at the ends. The two bones are bound together by a ligamentous band. It also articulates superiorly with the distal end of the humerus, and inferiorly with the carpus. When the wing is folded the radius is superior and a trifle to the inner side of the ulna.

_Description._—The proximal end is most expanded, and is obliquely truncate for the articular excavation adapted to the ulnar tubercle of the humerus. A short angular process behind the cavity represents the _olecranon_, which is the _processus olecranalis coracoideus ulnæ_ to which the ligamentum capsulare cubiti attaches. On the inner side of the head is the internal tubercle of the ulna and on the external side the external tubercle of the ulna. An excavation is noted on the radial side of the proximal end for the lateral articulation of the head of the radius. On the upper side near the articular part is located the _sigmoid cavity_.

The shaft, or corpus ulnæ, decreases in size near the distal end. It is slightly curved, flattened laterally with an internal and an external ridge.

The distal end of the ulna is slightly expanded into a _trochlea_ which is sharply convex and articulates with two free carpal bones, the scapho-lunar, or os carpi radiale, and the cuneiform, or os carpi ulnare. The scapho-lunar is placed on the radial side, and the carpiulnare on the ulnar side. The distal extremity of the ulna is provided with a _styloid process_ and on the dorsal side with a _tubercle_.

=The Radius.= _Location._—The radius lies beside the ulna with which it articulates at each extremity. At the inferior extremity the articulation is rotary. It also articulates superiorly with the humerus and inferiorly with the os carpi radiale.

_Description._—The radius, cylindrical in shape, is more slender than the ulna.

The proximal end is expanded, subelliptical, with a concavity for the oblique tubercle and a thickened convex border for articulation with the ulna. This end is provided with the _tuberositas radii_.

The shaft, or corpus radii, is slender, subcompressed, and has a slight bend upward from the ulna. A nutrient foramen occurs in this shaft.

The distal end is expanded and rather flattened with two grooves on the anconal side for passage of tendons. For articulation with the scapho-lunar the radius is provided with a terminal _transverse convexity_ produced palmad, which also articulates with the ulna laterally. There is a tuberosity on the radial side of the expansion and inferiorly the _inferior tuberculum ossis carpi radialis_ and superiorly a _superior tuberculum ossis carpi radialis_.

=The Hand.=—The hand is made up of the carpus, the metacarpus, and the phalanges.

The bones of the hand are so arranged as to allow abduction and adduction, or flexion in the ulno-radial plane, movements which are necessary in the outspreading and folding of the wing. Thus the hand of the fowl moves in a state of pronation, without the power of rotation. The carpal bones are so placed between the anterior arm and metacarpus as to reduce the abduction which is necessary to hold and extend the wing, so that the hand or wing be in a fixed position.

=The Carpus.=—The carpus in the domestic fowl is represented by two bones, ossa carpi, called the _scapho-lunar_, or _os carpi radiale_, and the _cuneiform_, or _os carpi ulnare_. The scapho-lunar is the smaller and is located between the radius and metacarpus. The cuneiform is the larger and is located between the ulna, the radius, and the metacarpus. The cuneiform is somewhat anvil-like in shape, being provided with a body and two prongs.

=The Metacarpus.=—The metacarpal bones, or ossa metacarpi, two in number, are separated at their middle portion, and consolidated at their extremities. The upper proximal base of the metacarpus is provided with a tubercle, the tuberculum muscularis, and externally the tuberculum ulnare ossis metacarpi. The distal end of the metacarpal bone is provided with a tuberculum articulare.

=The Phalanges.=—The first three fingers only are represented, and these are rudimentary.

The first finger called the pollex or thumb, consists of but one joint. It is located on the proximal and outer end of the metacarpal bone. It has on its proximal end a tubercle, the tuberculum articulare.

The second finger, the best developed, consists of two phalanxes. These are the main bones extending from the metacarpus. Each articular end is provided with a _tuberculum articulare_.

The third finger, small, cylindrical in shape, is located at the distal and inner side of the metacarpal bone.

=THE PELVIC GIRDLE= (Fig. 4, No. 25; Fig. 5, Part II, 6)

The pelvic girdle is made up of three bones as follows: the ilium, the ischium, and the pubis, all of which are fused in adult life. They are separate in the baby chick (Fig. 5, Part II, 6). The pelvis together with the lumbo-sacral vertebræ forms a thin, irregular, shell-like structure extending superiorly from the tail to the thoracic region. The sacrum is broad posteriorly and together with the ilium forms the pelvic roof. The ilium and ischium are its lateral walls.

The top surface of the pelvis shows the _fovea ilio-lumbalis dorsalis_, which is bounded mesially by the crista ilii. Between it and the spina lumbalis there is a broad furrow, the bottom of which is formed by the dorsal surface of the lumbar vertebræ. The _sulcus ilio-lumbalis dorsalis_ is formed by the rims of the ilia, so that a ridge is observable. The _cavum ilio-lumbale dorsale_ is formed by the iliac rims on either side. Anteriorly is the _canalis ilio-lumbalis_, which is formed by the ilium and the lumbar vertebral spines. It is located longitudinally to the vertebræ. The anterior opening of this canal is the larger. Posterior to the _acetabulum_ is the _post-acetabular_ ridge.

The under part of the pelvis presents three distinct regions. The cavity is divided into the _fovea lumbalis_, or anterior part, the _fovea ischiadica_, or mesial part, and the _fovea pudendalis_, or posterior part. Posterior to these is the region called the _planum coccygeum_.

The fovea lumbalis contains the anterior lobe of the kidney, and is circumscribed anteriorly by the last rib-carrying vertebra, and posteriorly by the transverse process of the last lumbar vertebra.

In the fovea ischiadica which follows, lie the nerve plexus ischiadicus and the middle lobe of the kidney. Its posterior boundary is the linea arcuata. The linea arcuata is a line drawn from the acetabulum of the one side to the acetabulum of the other side.

The fovea pudendalis contains the posterior lobe of the kidney. The posterior boundary is the anterior border of the first coccygeal vertebra. It gives passage to the nerve plexus pudendo-hemorrhoidalis.

The ilium, the ischium, and the pubis join to form the cotyloid cavity, or acetabulum, in which articulates the head of the femur. The floor of the cavity is perforated by a relatively large round foramen.

=The Ilium.= _Location._—The ilium, together with the lumbo-sacral vertebræ, forms the roof of the pelvic cavity. It articulates at its inner border with the lumbo-sacral vertebræ, postero-laterally with the ischium and at the cotyloid cavity with the pubis.

_Description._—The ilium is remarkable for its development in the long axis of the vertebral column. It is long and narrow; and mesially, where it is thickest it forms the upper wall of the acetabulum. Anterior to the acetabulum it is outwardly concave, and posterior to the acetabulum it is convex. The ilium fuses with the last dorsal vertebra and with the lumbo-sacral vertebræ and is excavated on its internal face. This surface is irregular and lodges the kidneys. This inner margin of the renal part enters with the square extensions of the posterior excavation passing into the posterior iliac spine. The external margin is the extension of the crista transversa and forms the _processus ischiadicus_. Posteriorward the renal part of the ilium joins the ischium.

The ilia converge at the summits of the anterior sacral spines forming the _ilio-lumbar_ spines.

The ilium is joined to the square extensions of the last sacral vertebra by the _symphysis ilio-sacralis_, to the larger part of the lumbar vertebræ by the _sutura ilio-lumbalis_, and to the transverse processes of the last sacral vertebræ by the _symphysis ilio-sacri_.

=The Ischium.= _Location._—The ischium is located in the postero-inferior part of the pelvis. It joins superiorly with the ilium, and inferiorly with the pubis.

_Description._—The ischium is smaller than the ilium and is a flattened, triangular-shaped bone, thickest where it forms the posterior part of the acetabulum, becoming thinner and broader as it extends backward. Posteriorly it forms the caudal extension. The inferior border is turned slightly outward and is fused with the pubis. Between these bones there is located the large oval _ischiadic foramen_, through which passes the ischiadic nerve. This bone aids the ilium in the formation of the obturator foramen through which passes the tendon of the internal obturator muscle. The lower part of the ischium which separates the ischiadic foramen from the obturator foramen is called the _ramus ascendens ossis ischii_.

=The Pubis.= _Location._—The pubis is located along the inferior margin of the ischium and extends further back than the posterior border of the ischium.

_Description._—The pubis is a long, slender, rib-like bone. It forms the lower and front portion of the acetabulum. The ischiadic foramen formed by the ischium and pubis is single and nearly circular in fowls, double in pigeons, and in geese and ducks it is elongate.

THE HIND LIMB (Fig. 4, Nos. 35, 47, 48, 49, 50, 51, 52, and 53; Fig. 12)

The pelvic, or hind, limb supports the body. The bones of each leg are the femur, which constitutes the thigh, the tibia and the fibula, which represents the leg, and the metatarsus and the phalanges, which form the foot.

=The Femur= (Fig. 12, _A_ and _B_). _Location._—The femur, or os femoris, the first bone of the hind extremity, extends obliquely downward and forward, articulating with the acetabulum above and the tibia, the fibula, and the patella below.

_Description._—The femur, one of the largest, thickest, and strongest bones of the body, belongs to the class of cylindrical bones, and presents for examination a shaft and two extremities.

The superior, or proximal extremity, is provided with a head, caput femoris; the neck, collum femoris; and the trochanter. The head is relatively small, and is marked by a depression above for the round ligament which fills the cavity in the acetabular wall. Its axis is nearly at right angles with the shaft. A neck joins it to the body at the proximal end. External to the head of the femur is the _trochanter_. The trochanter presents an outer convexity over which the tendon of the gluteus maximus extends to become inserted below. The _trochanteric ridge_, which is opposite the articular head, presents an outer flattened surface which possesses impressions for muscular attachments. The _trochanteric fossa_, or fossa trochanterica, is shallow.

The _shaft_, or _corpus femoris_, is shorter than the tibia, is in general cylindrical, bent forward, and the lower half is flattened and expanded transversely. A nutrient foramen is located in the median portion of the shaft. The shaft shows muscular linear ridges.

The distal extremity is large in both directions and comprises the _trochlea_ in front and two _condyles_ behind, one internal and one external. The condyles are separated by the _intercondyloid fossa_, or _fossa intercondyloidea_, which is marked with pits for the attachment of ligaments; and above this is the _epitrochlear fossa_.

[Illustration:

FIG. 12.—Bones of the hind extremity.

_A._ Posterior view of femur.

_B._ Anterior view. 1, Shaft. 2, Proximal extremity. 3, Distal extremity. 4, Articular head. 5, Trochanter major. 6, Shallow trochanteric fossa. 7, Convexity over which the tendon of the gluteus maximus glides. 8, External condyle. 9, Internal condyle. 10, Nutrient foramen. 11, Intercondyloid fossa. 12, Muscular linear ridges. 13, Epitrochlear fossa.

_C._ Internal view of tibia.

_D._ External view. 1, Shaft. 2, Articular head. 3, Distal end. 4, The rotular process. 5, The fibular ridge. 6, External condyle. 7, Internal condyle. 8, Intercondyloid space. 9, Nutrient foramen.

_E._ Fibula, lateral view. 1, Articular head. 2, Its attenuated portion.

_F._ Posterior view of metatarsus. 1, Trochlea for inner or second digit. 2, Trochlea for middle or third toe. 3, Trochlea for outer digit. 4, Bony core for spur. 5, Bony canal for tendons. 6, Groove for tendons. 7, Fossa intercondyloidea. ]

The _inner condyle_ begins anteriorly as a ridge, and expands into a convexity which attains its greatest breadth posteriorly where it becomes more flattened. The inner side of the inner condyle is flattened and is provided with a tuberosity at its mid-part and a second just above the posterior part of the condyle.

The _outer condyle_ is formed in the same manner as the inner condyle. It is indented at its broad, lower end by an _angular groove_, which, winding divides the posterior part of the condyle into two convexities. The more external convex ridge and the groove dividing it from the outer condyle are adapted to the head of the fibula. There is in this part a _fibular ridge_ and above this ridge a tuberosity.

=The Tibia.= _Location._—The tibia (Fig. 12, _D_ and _C_) extends obliquely downward and backward from the knee-joint to the hock. It articulates above with the femur and, by its procnemial process with the patella, below with the metatarsus, and laterally with the fibula.

_Description._—The tibia is the longest bone in the posterior limb, and possesses a shaft and two extremities. It is largest at the proximal end and presents three faces.

The proximal extremity presents a semi-oval articular surface, not quite at right angles with the shaft, which articulates with the condyles of the femur. The margin is raised toward the anterior of the bone. The _head of the tibia_, or _caput tibiæ_, extends into a rotular process which extends transversely, and is truncate. From the anterior of this process there descends two vertical ridges; one near the angle of the rotular process, the _procnemial ridge_; the other from the outer fibular angle, the _ectocnemial ridge_. On the outer side of the intercondylar tuberosity there is a surface for the ligamentous union with the head of the fibula; and a short distance below this there is a vertical ridge for the close attachment, almost a fusion, with the fibula, called the _fibular ridge_.

The _shaft_, or _corpus tibiæ_ is straight and the upper two-thirds subtrihedral; the lower third oval. A _nutrient foramen_ occurs near the upper postero-internal portion of the middle third of the bone.

The distal extremity is much smaller than the proximal one; it is quadrangular in form. The expanded inferior end of the tibia forms two articular condyles above which posteriorly there is the _epicondyloid fossa_. The inner condyle, the larger, has a groove near the lower end of the anterior part of the shaft, which deepens toward the intercondyloid space. This _intercondyloid fossa_ in young birds is covered by a strong ligament, which in older birds, becomes ossified. On the lateral side of each condyle, there is a depression for the attachment of ligaments.

=The Patella.= _Location._—The patella, or knee-cap, thin and wide, articulates with the procnemial process of the tibia, and with the deep trochlea of the distal end of the femur.

_Description._—The patella is irregular in shape with three faces and three borders. The posterior surface is articular. The other two surfaces are rough for tendinous attachment. The patellar ligaments in old birds may become ossified.

In order to turn the foot in and out, the tibia not only turns around the inner condyle of the femur, but also around the patella, so that the posterior surface turns outward and thus turns outward the metatarsus and all the toes.

=The Fibula.= _Location._—The fibula lies at the outer border of the tibia. It articulates superiorly with the outer condyle of the femur, and laterally with the tibia.

_Description._—The fibula is rudimentary; it is largest superiorly and tapers to a slender point. The head is compressed laterally, and furnishes an upper and an inner articular surface.

=The Tarsus.=—There exist, during fetal development of the chick, two rows of tarsal bones which later become fused. The upper row fuses with the tibia and the lower with the metatarsus. Therefore, in the adult, there is no tarsus.

=The Metatarsus.= _Location._—The metatarsal bone extends downward and forward. In birds it consists of one bone, which articulates superiorly with the inferior extremity of the tibia. On the distal end it has a threefold trochlear arrangement which articulates with the three principal digits.

_Description._—The proximal extremity posteriorly has a process which may be considered as a consolidation of originally separate metatarsal bones. The process at the supero-posterior part of the metatarsus is called the _hypotarsus_ of the _tarso-metatarsus_, through which extends a canal called the _hypotarsal canal_, and which gives passage to flexor tendons.

The proximal end of the metatarsus is ossified from one center of ossification forming an epiphysis which caps the ends of the three original metatarsal bones that coalesce, first with one another, then with the epiphysis, thus forming a single compound bone. Above and just to the inside of the metatarsus there may occur a small bone which is imbedded in ligaments and articulates with the inner proximal surface of the metatarsus. This has been called by Gadow a _sesamoid bone_.

The shaft shows _tendonal grooves_ which are best marked on the posterior surface. The shaft is rounded at the sides and flattened on the anterior and posterior surfaces. At the juncture of the middle and inferior thirds of the metatarsus there is a conical process turned slightly backward, which serves as a base for the _spur_. The spur is a horny structure.

At the distal extremity occurs the threefold trochlear arrangement mentioned above, which incloses the fossa intercondyloidea. The inner trochlea is the broadest, and the outer the narrowest. The inner trochlea articulates with the proximal end of the second, the middle with the third, and the outer with the fourth toe.

=The Phalanges.= _Location._—Most domestic fowls are provided with four digits, or toes; the Houdan and Dorking are provided with five. In fowls with four toes the three principal toes, the second, the third, and the fourth, are directed forward, and the first, or hallux, is directed backward.

_Description._—The last phalanx of each toe, called the ungual phalanx, is slightly curved downward, is pointed anteriorly, like the claw of the cat or dog, and is covered with a horny sheath. The articular ends of the joints of the phalanges are enlarged. The base of the basal phalanx has two enlargements, the superior-inferior tubercles, or tuberculum superius et inferius, between which is located the fossa articularis transversa. Laterally the head has two condyles, condyli laterales, which are divided by the sulcus longitudinalis. The bodies of the phalanges vary in form; they are superiorly rounded, but inferiorly rounded, flat, or even somewhat concave. The distal extremity has an articular trochlea.

The _first toe_, or digit, called the _great toe_, or _hallux_, is composed of three phalanges, or segments. The first segment, or basal phalanx is considered a rudimentary metacarpal bone; it is attached by a fibrous cartilaginous tissue to the inner posterior surface of the inferior extremity of the metacarpal bone just below the spur.

The _second toe_, likewise composed of three phalanges, is directed forward. It articulates with the inner trochlea located on the inferior metacarpal bone.

The _third toe_, made up of four phalanges, is the middle of the three forward toes. It articulates with the middle trochlea of the inferior extremity of the metacarpal bone.

The _fourth toe_, is composed of five phalanges; it is, however, of approximately the same length as the third, the segments being shorter. The fourth or outer toe articulates with the outer trochlea of the distal extremity of the metacarpal bone.

Arthrology

=Kinds of Joints.=—Joints may be movable, immovable, or mixed. In _movable_, or _true joints_ the articular surface of each bone is covered by cartilage. The bones are held together by ligaments, the capsular one often surrounding the joint and enclosing the synovial membrane. In some joints there is a pad of fibrous cartilage interposed between the two articular cartilages. Such a pad, called a _meniscus_, adds to the elasticity and the free movement of the joint. Movable joints form the most numerous class; they are for the most part found in the limbs.

In an _immovable joint_ there is only a thin layer of fibrous or cartilaginous material interposed between the bones. The fibrous layer of the periosteum of both bones unite to cover the connecting material and becomes attached to the same, thus serving as a ligament. If the connecting material is fibrous, the joint is called a _suture_; if cartilaginous, a _synchondrosis_. These joints are found in the skull and in the pelvis.

The term _mixed_ is used with reference, not to the motion in joints, but to their structure, which partakes of the nature of both the movable and immovable. The bones are firmly joined by a strong interposed pad of fibrous cartilage to which also is adherent the ligaments of the joint. There are no capsular ligaments; the cartilaginous pad or disc is softer toward its center, where occasionally there may be one, or even two, narrow cavities. Authorities differ as to whether such cavities are lined by synovial membrane or not. Since there are really no frictional surfaces in such a joint, motion depends upon the flexibility of the disc. The joints between the vertebral centra afford the best illustration of the mixed class.

=Movement of Joints.=—The movements admissible in joints may be divided into four kinds: gliding, angular movement, circumduction, and rotation. These movements are often, however, more or less combined in the various joints. It is seldom that there occurs only one kind of motion in any particular joint.

_Gliding movement_ is the most simple kind of motion that can take place in a joint, one surface gliding or moving over another without any angular or rotary movement.

_Angular movement_ occurs only between the long bones. By it the angle between the two bones is increased or diminished. It may take place in four directions: forward and backward, consisting of flexion and extension; or inward and outward from the medial line of the body, consisting of adduction and abduction. Abduction of a limb is movement away from the medial line of the body. Adduction of a limb is movement toward the medial line of the body.

_Circumduction_ is that limited degree of motion which takes place between the head of a bone and its articular cavity, whilst the extremity and sides of the limb are made to circumscribe a conical space, the base of which corresponds with the inferior extremity of the limb, the apex with the articular cavity; this kind of motion is best seen in the shoulder- and hip-joint.

_Rotation_ is the movement of a bone upon an axis, which is the axis of the pivot on which the bone turns, as in the articulation between the atlas and axis, when the odontoid process serves as a pivot around which the atlas turns; or else is the axis of a pivotlike process which turns within a ring, as in the rotation of the radius upon the humerus.

_Pronation_ is a form of rotation in which the inferior extremity of the radius passes before the ulna, and thus causes the hand to execute a kind of rotation from without inward.

_Supination_ is a form of rotation in which the movement of the forearm and hand are carried outward so that the anterior surface of the latter becomes superior.

=The Ligamentous Structure.=—Ligaments are dense, fibrous, connecting structures. They are made up principally of white fibrous tissue and exist in all true joints.

There are four kinds of ligaments associated with true joints:

The first kind, the _capsular ligament_ which encloses all true joints, is thin and consists of interlaced fibers attached to the bone at the edges of the articular cartilages. It either partly or wholly surrounds the joint, enclosing and protecting a synovial apparatus, which, by secreting a liquid resembling serum, lubricates the joint to prevent friction.

The second kind, the binding or _lateral ligaments_, consist of flattened or rounded cords or bands of fibrous tissue. Such a ligament extends from one bone to the other, and firmly attached to their roughened surfaces, holds the bones in place and at the same time allows the required amount of motion.

The third kind, located between the joints, is called _interosseous ligament_.

The fourth kind, called the _annular ligament_ binds down and protects the tendons.

=Ligaments of the Ear[2].=—The concha of the ear is provided with a superior and an inferior ligament.

Footnote 2:

The classification of Gadow is used.

=Ligaments of the Jaw.=—The articulations of the lower jaw are complex. The freely movable articulation is between the inferior maxilla and the quadrate. Less freely movable articulations are formed by the quadrate with the temporal, the zygomatic and the pterygoid. A lateral ligament of the jaw, the _articulo-jugale_ extends from the posterior border of the inner wing of the os articulare of the inferior maxilla (Fig. 8, No. 10, and Fig. 19, No. 15) to the outer border of the os quadrato jugulare.

A _lateral temporo-maxillary ligament_ extends from the outer surface of the temporal bone to the outer border of the os articulare of the inferior maxilla (Fig. 8, No. 11, and Fig. 19, No. 14).

=Ligaments of the Vertebræ.=—In each space between the bodies of the vertebræ there is a _meniscus intervertebralis_. This meniscus is analogous to the annulus fibrosus of mammals (Gadow), which, is possibly formed as a protrusion of the anterior surface of the vertebral body. The meniscus or disc may develop into a ring-shaped structure, the true meniscus, or it may develop to different degrees as an extension of the vertebral body surface, and become, as in the dorsal and lumbar regions, fused with the vertebral segments, in which case it is called the annulus fibrosus.

The vertebral disc which is connected with the atlas and which is fused with that bone, represents the first meniscus, which is called the _ligamentum transversum atlantis_. This, as well as other ligaments of the spinal column, may become ossified.

The ligament which is located between those vertebral bodies which face each other and is inside the joint cavity, is called the _ligamentum suspensorium corporum vertebralium_. It passes through the central opening of the meniscus and lies exactly in the long axis of the body of the vertebra.

The first ligament of the neck is the _ligamentum suspensorium dentis epistrophei_. The _ligamentum capsulare atlantico-occipitale_ and the _ligamentum capsulare atlantico-epistrophicum odontoideum_ are two parts of the joint capsule of the vertebral body. Other ligaments of this part are the _membranæ obturatoriæ intervertebrales posteriores_, which are located between the semicircular rims of the neck vertebræ.

The _ligamentum transversum atlantis_ surrounds the occipital condyle.

The _ligamentum nuchæ_ is a thin, membranous, ribbon-like structure which lies between the muscles of the right and those of the left side of the middle, and the lower part on the posterior of the neck, and ends in attachments to the superior spines of the cervical vertebræ.

The _ligamentum elasticum interspinale profundum_ and the _ligamentum elasticum interspinale superficiale_ and the three last named are the ligaments which keep the neck of the fowl in the s-shape, without the action of the muscles.

The _ligamentum capsulare obliquum_ connects the facets of the oblique processes.

=Ligaments of the Ribs.=—The thick inferior end of the sternal portion of the true rib has two small articular heads, which articulate with two depressions in the articular surface of the sternum. This articulation is held firm by a _capsular ligament_.

The upper end of the sternal rib forms an almost perfect right angle with the inferior end of the dorsal rib with which it is connected by a joint provided with a synovial apparatus and a capsular ligament. This arrangement allows free movement outward and inward and is the main joint in respiration.

The upper end of the dorsal portion of the rib articulates with the dorsal vertebra. The joint formed by the articular head with the body of the vertebra is provided with a capsular ligament. The tubercle of the rib articulates with the facet on the transverse process of the dorsal vertebra, and is provided with a transverse ligament, called the _ligamentum transversum externum_. It is also provided with a capsular ligament.

The _ligamentum triangulare_ connects each processus uncinatus with the succeeding rib. This ligament is in the form of a membranous sheet, or aponeurosis.

=Ligaments of the Sternum= (Fig. 13).—The external and the internal notches of the sternum are bridged over with a thin membrane which gives an extensive surface for muscular attachments. The sternal muscles overlie this portion.

[Illustration:

FIG. 13.—Muscles of the fore extremity. Inside view. 1, Lateral external process of sternum. 2, Lateral internal process of same. 3, Ligament of the external notch. 4, Ligament of the internal notch. 5, Pectoralis major. 5_a_, Its fan-shaped expansion at shoulder-joint laid back. 6, Pectoralis tertius. 7, The coracoid. 8, Biceps. 8_a_, Its long head. 8_b_, Its short head. 9, Pectoralis secundus. 10, Rectus abdominis. 11, Teres et infraspinatus. 12, Deltoid. 13, Capsular ligament. 14, Teres minor. 15, Coraco-brachialis. 16, Serratus magnus anticus. 17, Extensor metacarpi radialis longior. 18, Pronator brevis. 19, Flexor carpi ulnaris. 20, Flexor carpi ulnaris brevior. 21, Flexor digitorum profundus. 22, Extensor indicis longus. 23, Extensor ossis metacarpi pollicis. 24, Humerus. 25, Shoulder. 26, Elbow. 27, Carpus. 28, Section through vertebra. 29, Keel of sternum. 28_a_, Flexor brevis pollicis. 29_a_, Extensor proprius pollicis. 30, Flexor minimi digiti brevis. 31, Interosseous palmaris. 32, Interosseous palmaris. ]

The sternum is connected by a fibrous mass with the inferior portion of the clavicle, or hypocledium (Fig. 57), the _claviculosternal ligament_.

The inferior narrow elongated end of the coracoid forms with the sternum a true articulation, which is provided with a capsular ligament, the _ligamentum capsulare_. Capsular ligaments occur at the articulations between the sternum and ribs.

=Ligaments of the Shoulder-joint= (Fig. 13).—The shoulder-joint is made up of the scapula, the humerus, and the coracoid. The ends of these three bones form the _foramen triosseum_ (Fig. 15, No. _A_, 7) through which passes the tendon of the elevator muscle of the wing.

The furcula, independent of the shoulder-joint or girdle, is attached to the supero-internal part of the proximal end of the coracoid by fibrous connective tissue; it is also connected to the other bones of the shoulder-joint by the _ligamentum coraco-furculare_ and the _ligamentum furculo-scapulare_.

The _ligamentum coraco-scapulare_ extends from the tuberosity of the furcula to the coracoid and to the processus furcularis of the scapula.

The _ligamentum coracoido-scapulare externum_ extends between the external tuberosity of the coracoid, the tuberosity of the scapula, and the humerus.

The _ligamentum coracoideo-scapulare inferius_ extends from the coracoid to the inner tubercle of the scapula.

Another long, broad ligament belongs to the episternal apparatus.

The shoulder-joint is provided with a wide, loose, _capsular ligament_ (Fig. 13, No. 13). Attached to the humerus are four other ligaments, of which three pass from the anterior end of the coracoid and the fourth from the scapula. The latter are as follows: first, the _supero-anterior ligamentum humero-coracoideum_, which extends from the small tubercle of the humerus to the coracoid bone; second, the _antero-inferior ligamentum humero-coracoideum_, which extends from the humerus to the coracoid; third, the _ligamentum coraco-humerale_, which extends from the coracoid to the large tubercle of the humerus; fourth, the _ligamentum humero-scapulare_ which extends between the processus humeralis of the scapula and the head of the humerus.

=Ligaments of the Elbow-joint= (Fig. 14).—The elbow-joint is made up of the ulna, radius and the humerus. The ligaments of the elbow-joint are as follows: the _ligamentum capsulare cubiti_, or capsular ligament, which extends from the processus cubitalis of the humerus to the processus olecranalis coracoideus of the ulna and to the tuberositas radii of the radius (Fig. 15, No 5).

The _ligamentum laterale cubiti externum_ connects the outer humeral distal extremity with the head of the radius (Fig. 15, No. 2).

The _ligamentum laterale cubiti internum_ lies between the inner distal extremity of the humerus and the tuberculum internum of the ulna (Fig. 14, No. 9).

The _ligamentum annulare radii_ originates on the olecranon, surrounds the head of the radius, and is attached to the tuberculum internum of the ulna (Fig. 15, No. 3).

The _ligamentum cubiti teres_ extends from the head of the radius to the upper end of the ulna (Fig. 15, No. 4).

[Illustration:

FIG. 14.—Muscles and ligaments of the arm and forearm of a hen.

_A._ External view. 1, Expansor secundarium. 2, Tensor patagii longus. 3, Tensor patagii brevis. 5, Brachialis anticus. 6, Pronator longus. 7, Supinator brevis. 8, Extensor indicis brevis. 10, Scapulo-humeralis.

_B._ Internal view. 9, Ligamentum laterale cubiti internum. ]

The _ligamentum transversum_ spreads out between the head of the ulna and the radius, thus uniting the two bones, and limiting supination (Fig. 15, No. 1).

=Ligaments of the Carpal Joint.=—The carpal joint is made up of the ulna, radius, the two carpal bones and the metacarpus.

There are two strong _ligamenta obliqua carpi ulnaris_ which extend from the processus styloideus of the ulna to the tuberculum posterius carpi ulnaris of the os carpi ulnaris.

The _ligamentum posticum ulnare carpi ulnaris_ extends from the processus styloideus of the ulna to the os carpi ulnaris.

[Illustration:

FIG. 15.—Ligaments of the arm and forearm of a hen.

_A._ The scapulo-coraco-humeral articulation. 1, Proximal end of the humerus. 2, Articular head of humerus. 3, The coracoid. 4, Proximal end of the clavicle. 5, Tendon of pectoralis tertius. 6, Tendon of pectoralis secundus. 7, Opening or foramen triossium through which the tendon of the elevator of the wing passes. (Pectoralis secundus.) 8, Broken end of scapula.

_B._ 1, Ligamentum transversum. 2, Ligamentum laterale cubiti externum. 3, Ligamentum annulare radii. 4, Ligamentum cubiti teres. 5, A portion of the ligamentum capsulare cubiti. 6, Distal extremity of humerus. 7, Ulna. 8, Radius.

_C._ Muscles of the outside surface of the arm. 1, Tensor patagii longus. 2, Extensor digitorum communis. 3, Tensor patagii brevis. 4, Anconeus. 5, Flexor carpi ulnaris. 6, Biceps. 7, Triceps. 8. Deltoid. 9, Brachialis anticus. 10, Flexor metacarpi radialis. 11, Extensor ossis metacarpi pollicis. 12, Extensor metacarpi radialis longior. 13, Extensor indicis longus. ]

The _ligamentum ulnare carpi radialis_ is a short ribbon-like ligament which passes over the above-mentioned ligaments and is attached to the inner surface of the os carpus radialis.

The _ligamentum ulnare carpi radialis internum_ is a strong ligament which originates on the inner part of the elbow. It extends to the upper rim of the base of the main digit.

The _ligamentum radiale carpi radialis externum_ originates on the outside of the head of the middle digit and inserts to the superior tuberculum carpi radialis of the radius.

The _ligamentum carpi radialis internum_, a short ligament, extends from the inside of the head of the main digit to the inner rim of the carpi radialis.

The _ligamentum carpi interosseum_ is located between the carpal bones.

The _ligamentum ulnare metacarpi internum_ is spread out between the processus styloideus of the ulna and the tuberositas muscularis on the upper side of the middle finger base at a point where the second and the third metacarpi separate.

The _ligamentum ulnare metacarpi externum_ extends from the tubercle of the distal extremity of the ulna, on the dorsal side, to the tubercle on the base of the metacarpus.

_Ligamentum radiale metacarpi_ extends from the head of the inner digit to a point near the tuberculum muscularis of the radius.

The _ligamentum transversum ossis carpi radialis et metacarpi_ is located between the inferior tuberculum ossis carpi radialis and the first metacarpal bone.

There is another ligament between the tuberculum superiorus carpi radialis and the first metacarpal bone.

The _ligamentum ossis carpi radialis internum et metacarpi_ extends from the inner surface of the carpus radialis to the tuberositas muscularis of the radius.

The _ligamentum ossis carpi ulnaris externum et metacarpi_ extends from the ulnar carpal bone to the tuberculum of the metacarpal bone.

The _ligamentum ossis carpi ulnaris internum et metacarpi_ extends from the processus uncinatus of the ulnar carpal bone to the tuberositas muscularis of the metacarpal bone.

=Ligaments of the Finger.=—The _ligamentum pollicare_ connects the thumb with the first metacarpal bone.

The _ligamentum anterius ossis metacarpi et primæ phalangis digiti secundi_ extends from the tuberculum articulare metacarpi, of the proximal end of the metacarpus, to the tuberculum articulare of the first phalanx of the second or large finger. Similarly attached, are also an internal and a posterior ligament, or _ligamentum internum_ and _ligamentum posterius_.

The three phalanges are all provided with capsular ligaments, or ligamenta capsularia, which bind together the several phalanges.

The small or third finger is connected to the metacarpus by a capsular ligament, the _ligamentum capsulare_, and by an interosseous ligament, or _ligamentum interosseum digitorum_, to the first phalanx of the second finger.

=Ligaments of the Pelvis.=—The obturator foramen, formed by the ilium and the ischium, is covered by a broad membranous ligament (Fig. 4, No. 29).

The oblong foramen, or foramen oblongum, and the foramen ischiadicum, formed by the ischium and the pubis are covered by broad membranous ligaments (Fig. 4, Nos. 29 and 60).

_Poupart’s ligament_ or _ligamentum Poupartii_, quite small in fowls, extends from the anterior lower rim of the ilium to the pelvic cavity, and is inserted at the bottom of the acetabulum.

Another broad ligament originates from the posterior rim of the ischium and is attached to the square surface of the first coccygeal vertebra.

The _ilio-pubic ligament_ extends from the pubic spine to the last rudimentary rib.

=Ligaments of the Hip-joint= (Fig. 25, _F_).—The hip-joint is made up of the ilium, ischium, pubis and femur and is a deep ball-and-socket joint. The cavity or acetabulum is called a cotyloid cavity.

The hip-joint is provided with three ligaments.

The _ligamentum capsulare femoris_ is attached around the rim of the cotyloid cavity and around the rim of the articular head of the femur (Fig. 25, No. _F_, 4).

The _ligamentum teres_, or _round ligament_, is a very short ligament which closes the hole at the floor of the cotyloid cavity, at which point it is attached. It is also attached to the head of the femur.

The _ligamentum ilio-sacrale_ strengthens the hip-joint capsule. It passes from the lower anterior rim of the os ilii, extending over the capsule to the neck of the femur to which it is attached.

=The Ligaments of the Knee-joint= (Figs. 16 and 17).—The knee-joint is made up of the femur, patella, tibia and fibula, and is provided with the following ligaments:

The _ligamentum extero-laterale genu_ is a strong ligament extending from the condylus externus femoris, or external femoral condyle to the outer surface of the head of the fibula, or capitulum fibulæ. From this head there passes inward, a strong ligament to a point between the femur and fibula (Fig. 25, No. _D_, 4).

[Illustration:

FIG. 16.—Ligaments and muscles of the hind extremity.

_A._ A transverse section through the tibial or tarsal cartilage, front view. 1, Gastrocnemius tendon. 2, Flexor perforatus annularis primus pedis. 3, Flexor perforans digitorum profundus. 4, Flexor perforatus indicis secundi pedis. 5, Extensor longus hallucis. 6, The articular surface. 7, Ligamentum capsulare ossis tarsi. 8, Flexor perforatus medius secundus pedis. 9, Flexor perforatus indicis secundus pedis. 10, Tendons of the extensor muscles.

_B._ Knee-joint. Inside view of femoro-tibial articulation. 1, Anterior ligamentum cruciatum. 2, Internal ligamentum laterale genu. 3, Anterior patellar ligament. 4, Patella. 5, Distal end of femur. 6, Proximal end of tibia. 7, Location of meniscus or pad of fibrocartilage.

_C._ Anterior view of tibio-tarsal articulation. 1, Distal end of tibia. 2, Its articular surface. 3, Ligamentum anticum. 4, Proximal end of metacarpus. 6, Pad of fibrocartilage.

_D._ The dorsal surface of the coccyx. 1, The bilobate oil gland. 2, Its duct. 3, Levator coccygis.

_E._ Inside view of pelvis and thigh. 1, Obturator internus. 2, Ambiens. 3, Vastus internus. 4, Internal ligamentum laterale genu. 5, Tibialis anticus. 6, Loop through which the tibialis anticus passes. 7, Adductors of the thigh. 8, Loop for the extensor tendon. ]

The _ligamentum intero-laterale genu_ extends from the outer surface of the internal condyle of the tibia, or condylus internus tibiæ. It gives off a thin ligamentous slip which enters the joint and is attached to the inner half-moon shaped pad of fibrous cartilage, or meniscus, which it draws backward by the flexion of the knee (Fig. 16, No. _B_, 2).

The _ligamentum popliteum_ arises from the fossa poplitea of the distal extremity of the femur and extends downward to the posterior rim of the head of the tibia.

The _anterior ligamentum cruciatum genu_ originates from the fossa poplitea and extends outward antero-laterally to the rim of the head of the tibia (Fig. 25, No. 6).

The _posterior ligamentum cruciatum genu_ is a short, strong ligament which originates from the cavity of the internal condyle of the femur, or condylus internus femoris, and inserts into the internal glenoid cavity of the tibia (Fig. 25, No. 1) or cavitas glenoidalis interna.

The meniscus of the femoro-tibial articulation is divided into four parts, as follows: first, the _internal adhesio cornu antici cartilaginis lunatæ_; second, the _posterior adhesio cornu antici cartilaginis lunatæ_; third, the _external cornu cartilaginis lunatæ_; fourth, the _anterior cornu antici cartilaginis lunatæ_. The latter originates between the condyles and passes around the ligamentum cruciatum genu posticum (Fig. 16, No. _B_, 7).

The inner semi-lunar fibrous cartilage is well developed and is joined by two ligaments between the femoral and the tibial surfaces (Fig. 25, No. 1).

The external semi-lunar cartilage lies in a cavity between the external femoral condyle and the head of the fibula (Fig. 25, No. 2).

The fibrous cartilages are bound posteriorly by a ligament, and by a second ligament to the head of the fibula, or capitulum fibulæ. Both pads of fibrous cartilage are connected by a transverse ligament called the _ligamentum transversale commune_ (Fig. 25, No. 5).

The patella is provided with several ligaments, as follows:

The _anterior patellar ligament_, broad, strong, and irregular in thickness, extends from the inferior margin of the patella to the rim of the second tibial crest (Fig. 16, No. _B_, 3).

The _ligamentum capsulare capituli fibulæ_ is spread out between the head of the fibula, or capitulum fibulæ, and the superficies glenoidalis peronea tibiæ.

[Illustration:

FIG. 17.—Muscles and tendons of the head and posterior extremity.

_A._ Section of neck with superficial muscles removed. 1, Obliquo-transversales. 2, Interspinales. 3, Intertransversales. 4, Interarticulares.

_B._ Head showing muscles. 1, Beak. 2, Nostril. 3, Tongue. 4, Sublingual salivary gland. 5, Pterygoideus. 6, Stylo-hyoideus. 7, Temporal. 8, Flexor capitis inferior. 9, Rectus capitis lateralis. 10, Rectus capitis posticus major. 11, Trachelo-mastoideus. 12, Eye. 13, Mylo-hyoideus. 14, Genio-hyoideus. 15, Biventer maxilla. 16, Digastricus. 17, Rectus capitis anterior minor.

_C._ Foot of hen showing tendons. 1, Flexor perforans digitorum profundus. 2, Flexor perforatus medius primus pedis. 3, Sheath at joint through which tendon passes. 4, Flexor perforatus indicis primus pedis. 5, Flexor perforatus medius secundus pedis. 6, Flexor perforatus annularis primus pedis. 7, Flexor longus hallucis.

_D._ Outside view of leg of hen. 1, Biceps flexor cruris. 2, Semitendinosus. 3, Loop through which biceps flexor cruris passes. 4, Tibialis anticus. 5, Flexor perforatus indicis secundus pedis. 6, Flexor perforatus medius primus pedis. 7, Gastrocnemius. 8, Flexor perforatus annularis primus pedis. 9, Flexor perforatus medius secundus pedis. 10, Extensor longus hallucis. ]

The _ligamentum tibio-fibulare_ extends from the head of the fibula, or capitulum fibulæ, to the inner surface of the external crest, or crista externa tibiæ, of the tibia (Fig. 25, No. 3).

The _ligamentum interosseum_ is a delicate ligament located between the tibia and fibula (Fig. 25, No. 4) which very early becomes ossified.

=Ligaments of the Tibio-metatarsal Joint= (Fig. 16).—The tibio-tarsal joint is made up of the tibia and metatarsus.

The _ligamentum capsulare ossis tibio-metatarsi_ connects the tibia and the metatarsus and surrounds the joint (Fig. 16, Nos. _A_, 7 and _C_, 7).

The _ligamentum externum_, a long strong ligament, originates on the upper and outer surface of the external condyle, or condylus externus of the tibia and is attached to the upper rim of the os metatarsi (Fig. 23, No. 15).

The _ligamentum anticum_ is spread out between the fossa intercondyloidea of the tibia and the tuberculum ossis metatarsi of the proximal end of the metatarsus (Fig. 16, No. _C_, 3). Just posterior to this ligament, there is an interosseous ligament, the _ligamentum interosseum_.

A semi-lunar pad of fibrous cartilage, the _cartilago semi-lunaris_ is located between the outer distal extremity of the tibia and upper articular surface of the metatarsus (Fig. 16, No. _C_, 6). Its concave portion is directed anteriorly and receives an insertion from the ligamentum externum, or external ligament.

The tendon Achillis (Fig. 16, No. _A_, 1) may become ossified.

=Ligaments of the Toes= (Fig. 16).—In addition to the capsular ligaments, which all true joints have, we find the following in connection with the toes:

The _ligamentum superius_ and the _ligamentum inferius_ connect the second toe with the great toe, or hallux.

The _ligamentum laterale externum_ and the _ligamentum laterale internum_ unite the bases of the second, third and fourth toes to the lateral faces of the trochleas of the inferior extremity of the metatarsus.

The bases of the toes are held together by the _ligamenta transversa_. All the rest of the toes are held together by the _ligamenta capsularia digitorum pedis_ and by two lateral ligaments, namely: the _ligamentum laterale externum_ and the _ligamentum laterale internum_.

Myology

=Kinds and Structure of Muscles.=—Muscles are highly specialized structures which have the property of contractility when stimulated, and thus produce motion. Muscular tissue is sometimes called flesh. Two kinds of muscles are recognized; muscles of locomotion and visceral muscles.

The muscles of locomotion may be in masses of different shape attached to the skin, the _dermal_, or to the skin and skeletal structure, the _dermo-osseous_, or from one bone to another, the _skeletal_. The visceral muscles form sheets and make up a portion of the wall of many of the hollow organs, such as the intestines, the stomach, the gizzard, the esophagus, and the blood-vessels. A special type of muscle forms the heart.

When classified with reference to structure, muscular tissue is divided into three types, as follows: voluntary-striated, involuntary, and involuntary-striated. The microscopic examination of each of these types of muscle shows it to be made up of fibers, these fibers to be made up of muscle cells, the muscle cell to be inclosed in a delicate tubular sheath, or membrane, called the _sarcolemma_. This membrane, tough and elastic, isolates each fiber. The bundles of fibers, called _fasciculi_, are surrounded by a fibrous sheath, which is called the _perimysium internum_; and the entire muscle has likewise an investing sheath of connective tissue, called the _perimysium externum_. The muscular cells show a longitudinal striation marking the fibrillæ, and they also show a cross striation. Nuclei are found just beneath the covering, or sarcolemma, in the striated muscle cell (Fig. 77, No. 2). In the involuntary and in the involuntary-striated muscle cell, the nuclei are centrally located.

The _voluntary-striated muscles_ consist of cylindrical fibers and with a few exceptions, are under the control of the will. A muscle of this type, the regular skeletal form, usually has at each extremity a fibrous structure, called a tendon, by means of which it is attached to the bones. The intermediate fleshy portion of the muscle, in case of considerable bulk, is called the belly of the muscle.

The _involuntary_, _non-striated_, or _smooth muscle_, cells are spindle-shaped, long, and pale in color (Fig. 77, No. 1). The cells lie end to end forming fibers. These fibers do not terminate in tendons, but are arranged in sheets and aid in forming the walls of the digestive tract, to which they give the power of contraction and expansion.

_Involuntary-striated_, or _heart muscle_ (Fig. 77, No. 4), occupies an intermediate position between the two muscles just described. It is composed of cells which branch, are somewhat rectangular. They possess both longitudinal and transverse striation. Among the fibers is found a small amount of connective tissue, as in the former types of muscle, which gives support to the blood-vessels and nerves.

=Fascia.=—The term fascia is applied to membranous expansions, differing materially in strength, texture, and relations. Fascia is composed of loosely arranged white fibrous connective tissue. At least two layers may usually be distinguished, the superficial fascia and the deep fascia.

Below the skin is the _superficial fascia_, which forms a continuous covering over the whole body and serves to attach the skin to the underlying structure.

The _deep fascia_ more densely constructed, may be attached to the skeleton, ligaments, and tendons.

When the fascia spreads out, becomes denser, and acts as a continuation of a muscle, it is called an aponeurosis.

=The Muscular Nomenclature.=—In the fowl there are 162 muscles, single or in pairs. These muscles are named from their location, as the lingualis; others from their attachments, as the dermo-temporalis; some from their form, as the rhomboideus; others from their use, as the flexor or extensor; and still others from their direction, as the transversus.

The Dermal Muscles

Birds are provided with a system of delicate muscles divided into numerous fasciculi, which harmoniously act upon the feather quills and collectively agitate the plumage. These are the dermal muscles. This group is divided into two subgroups: the true dermal muscles, that is, those that have their origin and insertion to the under surface of the skin; and the dermo-osseous, those that originate on the surface of some bone and insert to the inner surface of the skin.

True Dermal Muscles

Dermo-frontalis Dermo-dorsalis Dermo-tensor patagii Dermo-humeralis Dermo-pectoralis

=Dermo-frontalis.=[3] _Location._—This muscle is somewhat rudimentary and may be entirely absent. It is located in the frontal region and is about 2 or 3 centimeters long and not so wide.

Footnote 3:

The classification of Shufeldt is used.

_Origin and Insertion._—Closely attached to the skin.

_Shape._—Flat and rather rectangular.

_Relations._—Superiorly with the skin and inferiorly with the frontal bones.

_Action._—By contraction the feathers on the top of the head lie flat. Those above the eyes are elevated.

=Dermo-dorsalis.= _Location._—In the median line of the neck and back.

_Origin and Insertion._—Adhering closely to the skin, it generally becomes lost at the occiput; it is most highly developed in the mid-cervical region, and it gradually disappears over the caudal region.

_Shape._—Delicate and ribbon-shaped.

_Relations._—Superiorly it is attached to the skin. Fat sometimes surrounds the muscle.

_Action._—By contraction it raises the feathers along the superior part of the neck and dorsal region.

=Dermo-tensor Patagii.= _Location._—Between the root of the neck and top of the shoulder.

_Origin and Insertion._—Attached to the skin in the region of the anterior part of the root of the neck, some fibers passing obliquely upward and blend with fibers of the dermo-temporalis. It blends, by a slender tendon, with that of the tensor patagii longus.

_Shape._—A bundle of muscular fibers later becomes thin, delicate, and triangular in shape.

_Relations._—Externally to the skin.

_Action._—Auxiliary to the tensor patagii longus. A tensor of this region.

The patagii are associated with the wing fold of skin which fills the angle between the arm and forearm. This fold contains elastic tissue and muscle.

=Dermo-humeralis.= _Location._—Lateral thoracic region.

_Origin and Insertion._—Fan-like delicate fibers from the skin in the abdominal integument, contracting into a long narrow fasciculus of fibers, again spreading out in fan-shape to be inserted to the tendon of the pectoralis major, just below its insertion.

_Shape._—Triangular, fan-shape.

_Relations._—Superiorly with the skin.

_Action._—Controls the skin in this region. The anterior end being fixed, the muscles are raised; and the posterior end acting as the fixed point, the feathers are caused to lie close to the body.

=Dermo-pectoralis.= _Location._—On each side of the chest, lying in a longitudinal manner.

_Origin and Insertion._—Attached to the skin on either side of the thorax corresponding to the dermo-dorsalis. Anteriorly it disappears over the region of the origin of the cleido-trachealis, and posteriorly just behind the tips of the post-pubic parts of the pelvis.

_Shape._—Thin, delicate.

_Relations._—Superiorly with the skin.

_Action._—The anterior part acting as the fixed point, the feathers of the chest are raised; and the posterior end acting as the fixed point, the feathers are made to lie flat.

The Dermo-Osseous Muscles

Dermo-temporalis Platysma myoides Dermo-cleido dorsalis Cleido-trachealis Dermo-spinalis Dermo-iliacus Dermo-ulnaris

=Dermo-temporalis= (Fig. 18, No. 1). _Location._—From the temporal region down the side of the neck to the anterior part of the thoracic region.

_Origin._—By a broad tendinous attachment from a small depression above and anterior to the temporal fossa. From here the fibers pass upward and backward and then downward.

_Insertion._—A few fibers blend with those of the cleido-trachealis. The fibers are then lost upon the skin in front and opposite the shoulder-joint. Some of the fibers blend with those of the dermo-tensor patagii.

_Shape._—Long, flat, and ribbon-shaped. The lower portion consists of delicate fibers.

_Relations._—Superior to the temporal muscle and sphenotic process. Superior to the cleido-trachealis and inferiorly to the shoulder-joint. The superior portion touches the skin throughout its entire length.

_Action._—A tensor of the lateral cervical integument. It is an auxiliary to the tensor patagii.

=Platysma Myoides.= _Location._—The inferior portion of the throat.

_Origin._—From the lower margin of the rami of the jaw. Just inferior to the attachment of the masseter.

[Illustration:

FIG. 18.—Muscles of the upper neck region, 1, Dermo-temporalis. 2, Cornu of the os hyoideum. 3, Carotid artery. 4, Jugular vein. 5, Pneumogastric nerve. 6, Esophagus. 7, Trachea. ]

_Insertion._—From the point of origin it spreads out into a thin fan-like layer and meets its fellow in the median raphe. It is attached to the skin in this region.

_Shape._—A very thin fan-shaped muscle.

_Relations._—Closely adherent to the skin.

_Action._—Assists in supporting the lingual apparatus and superior larynx. Compresses and elevates the part.

=Dermo-cleido Dorsalis.= _Location._—Anterior shoulder region.

_Origin._—From the upper mesial part of the clavicular bone.

_Insertion._—Three fasciculi forming a fan-like arrangement attached to the skin in the shoulder-joint and scapular region. The extremities of the fasciculi may meet in the median line of the dorsal region and merge with the dermo-dorsalis.

_Shape._—Three fasciculi forming a fan-shaped radiation.

_Relations._—Superiorly with the skin. Inferiorly with the shoulder-joint.

_Action._—Contracting with the origin as the fixed point, they brace the skin over the forepart of the back. With the integumental attachment as the fixed point, they aid in the act of respiration.

=Cleido-trachealis.= _Location._—Extending from the shoulder to the superior laryngeal region.

_Origin._—From a small area on the antero-inner part of the middle of the arm of the furcula.

_Insertion._—The fibers pass upward and become flattened and attached to the skin and dermo-temporalis muscle. They touch each other on the anterior border of the superior larynx, the trachea, and the skin over these parts.

_Shape._—A slender bundle of muscles.

_Relations._—Superiorly the skin, and internally the larynx and the trachea.

_Action._—Controls the skin region of this part of the neck.

=Dermo-spinalis.= _Location._—In the region of the shoulder.

_Origin._—In an attenuated fascia from the crest of the neural spines of the first, the second, and the third dorsal vertebræ.

_Insertion._—To the skin in a broad pale stratum, over the scapular region.

_Shape._—Thin, pale, and very delicate.

_Relations._—Superiorly with the skin, and inferiorly with the shoulder.

_Action._—Controls the skin of the region.

=Dermo-iliacus.= _Location._—Along the back on either side of the spine.

_Origin._—From the inner angle of the marginal portion of the antero-dorsal border of the ilium.

_Insertion._—Passing forward as a delicate band it spreads out and becomes lost in the skin of the shoulder region.

_Shape._—Thin, delicate, and ribbon-shaped.

_Relations._—Superiorly with the skin.

_Action._—If the posterior end is fixed, it will cause the feathers to lie close to the skin. Its action would then be opposite to the dermo-dorsalis.

=Dermo-ulnaris.= _Location._—Outer surface of the anterior upper costal and the posterior humeral region.

_Origin._—By a thin fascia from the outer part of the third and the fourth true ribs at the base of their epineural appendages. Also from the fascia between them.

_Insertion._—The fibers pass forward and upward as a thick muscular bundle and is loosely attached to the skin at a point just back of the humerus. The tendon later becomes spread out and attached to the fascia as far as the elbow-joint. It covers the olecranon of the ulna.

_Shape._—At first rather thick, fascicular-like; later becomes tendinous; and at its attachment it becomes spread out over the olecranon.

_Relation._—Inferiorly with the ribs and humerus, and externally with the skin.

_Action._—A depressor of the humeral region.

The Skeletal Muscles

The Muscles Of The Head

Temporal Masseter Biventer maxillæ Entotympanicus Pterygoideus internus Pterygoideus externus Digastricus

=Temporal= (Fig. 19, No. 4). _Location._—Occupies the temporal fossa.

_Origin._—From the mesian line of the sphenotic process, and the adjacent wall of the orbit.

_Insertion._—The fibers passing downward and forward blend with the fibers of the masseter. Inferiorly it inserts by a tendon to the coranoid process upon the superior ramal margin of the mandible.

_Shape._—Fan-shaped with broad portion uppermost.

_Relations._—It occupies the temporal fossa. It is related superiorly with the dermo-temporalis and skin. Inferiorly, with the biventer maxillæ and the masseter.

_Action._—It aids in closing the jaw.

=Masseter= (Fig. 19, No. 1). _Location._—Occupies the supero-lateral portion of the surface of the lower jaw.

_Origin._—In two portions: the first, by a broad and thin tendon from the entire length of the bony ridge above the external auditory meatus, from the squamosal process, and from the outer portion of the quadrate bone; the second, from the side and under border of the zygoma.

_Insertion._—The first portion: The fibers pass downward and forward beneath the zygoma; a few of the fibers blend with those of the temporal; one tendon inserts to a small tubercle on the upper border of the jaw behind the coronoid process, and by fleshy insertion to the outer side of the ramus of the lower jaw, quite as far forward as the horny portion of the beak. The second portion: by a small tendon to the mandible on its upper border immediately in front of the articular portion.

_Shape._—Flat, and elongate. Somewhat fleshy.

_Relations._—Superiorly with the temporal, and inferiorly with the biventer maxillæ and stylo-hyoideus. Externally with the skin, and internally with the jaw bone.

_Action._—Aids in closing the jaw.

=Biventer Maxillæ= (Fig. 19, No. 3). _Location._—Covers the outer posterior portion of the mandible.

_Origin._—It arises in two portions: The first, from a ridge bounding the posterior part of the auditory canal; the second, from a depression of the mesial side. These two parts blend and extend downward and forward.

_Insertion._—To the posterior part of the articular end of the mandible.

_Shape._—A curved fleshy mass.

_Relations._—Superiorly with the temporal and stylo-hyoideus. Posteriorly with the digastricus and genio-hyoideus. Internally with the jaw bone, and externally with the skin.

_Action._—It aids in opening the jaw.

=Entotympanic.= _Location._—Posterior to the pterygoid.

_Origin._—From the side of the basi-sphenoid and from the base of the rostrum immediately beyond it.

_Insertion._—The fibers pass downward and forward, and insert by a double tendinous slip. One slip inserts to a spine-like process on the upper side of the pterygoid, and the other to the quadrato-pterygoidean articulation.

_Shape._—Spindle-shaped.

_Relations._—Anteriorly with the pterygoid. Internally and posteriorly with the basi-sphenoid. Externally with the pterygoideus internus.

_Action._—Aids in raising the upper mandible by pulling forward the quadratus and pterygoidean against the palatines.

=Pterygoideus Internus= (Fig. 17, No. _B_, 5). (Synonym.—Pterygoideus medialis.[4])

Footnote 4:

According to international veterinary nomenclature.

_Location._—A muscular mass at the roof of the mouth.

_Origin._—From the major part of the surface of the palatine bone and the distal head and shaft of the pterygoid and the sphenoidal projection.

_Insertion._—By a tendon to the antero-internal part of the articular part of the mandible.

_Shape._—Fusiform with a thick fleshy belly.

_Relations._—Superiorly with the palatine, the pterygoid, and the sphenoid bones. Inferiorly with the skin.

_Action._—It aids in closing the jaw.

=Pterygoideus Externus.= (Synonym.—Pterygoideus lateralis.)

_Location._—Supero-external to the pterygoideus internus.

_Origin._—From the outer part of the extremity of the orbital process of the quadrate.

_Insertion._—The fibers pass downward, outward and forward and are inserted to the inner part of the mandibular ramus.

_Shape._—A small round bundle.

_Relations._—Inferiorly with the pterygoideus internus. Externally with the inferior maxilla.

_Action._—Aids in closing the jaw.

=Digastricus= (Fig. 17, No. _B_, 16). _Location._—Extends from the basi-temporal to the side of the neck.

_Origin._—From the external lateral angle of the basi-temporal.

_Insertion._—Opposite the angle of the jaw the fibers spread out in fan-like arrangement. The muscle meets its fellow of the opposite side; extends longitudinally over the superior larynx, for some distance down the neck.

_Shape._—Thin and ribbon-shaped.

_Relations._—Externally to the platysma myoides. The anterior fasciculi blend with those of the mylo-hyoideus; internally with the larynx at the upper part.

_Action._—To raise the trachea and hyoid apparatus against the pharynx.

The Muscles Of The Tongue

Mylo-hyoideus Stylo-hyoideus Genio-hyoideus Cerato-hyoideus Sterno-hyoideus Depressor-glossus Cerato-glossus Hyoideus transversus

=Mylo-hyoideus.= _Location._—The forepart of the inter-ramal space.

_Origin._—From the inner side of the lower jaw at a point just above the lower border and the inturned edge of the horny sheath of the beak.

_Insertion._—By aponeurosis to the under side of the hyoid, on the median line between the first and the second basi-branchial.

_Shape._—Thin, flat, and delicate.

_Relations._—Inferiorly with the skin. Thin and rather broad, it meets its fellow of the opposite side. Laterally with the rami of the jaw. Superiorly with the hyoid apparatus.

_Action._—Lifts the tongue upward against the roof of the mouth.

=Stylo-hyoideus= (Fig. 17, No. _B_, 6). _Location._—Supero-posterior to the hyoid apparatus.

_Origin._—From the outer portion of the articular enlargement of the lower jaw.

_Insertion._—By a tendon to the basi-branchial of the thyro-hyal.

_Shape._—A long transversely flattened fasciculus.

_Relations._—Supero-posterior part of the hyoid apparatus along side the genio-hyoideus and the cerato-hyoideus.

_Action._—Singly, pulls the tongue to one side; acting with its fellow, pulls the tongue upward.

=Genio-hyoideus= (Fig. 9, No. 7). _Location._—Supero-posterior to the hyoid apparatus.

_Origin._—From the anterior portion of the inner side of the lower jaw.

_Insertion._—To the middle of the outer side of the basi-branchial of the corner of the os hyoides which cornu it completely envelops.

_Shape._—A long, rather thick fasciculus.

_Relations._—With the stylo-hyoideus and cerato-hyoideus.

_Action._—Protrudes the tongue from the mouth.

=Cerato-hyoideus= (Fig. 9, No. 8). (Synonym.—Kerato-hyoideus.)

_Location._—Inferior to the hyoid apparatus.

_Origin._—By a delicate tendinous slip from the under side of the shaft of the basi-hyal element of the hyoid apparatus.

_Insertion._—To a small elevation on the under side of the anterior end of the glosso-hyal.

_Shape._—A small round muscular fasciculus becoming tendinous in its anterior half.

_Relations._—Superiorly with the hyoid apparatus.

_Action._—Singly, pulls the tongue to one side; acting with its fellow, depresses the tongue.

=Sterno-hyoideus.= _Location._—Inferior to the hyoid apparatus.

_Origin._—From the outer anterior surface of the thyroid bone of the superior larynx.

_Insertion._—To the anterior part of the basi-hyal.

_Shape._—At first broad and rather fleshy, becomes contracted and somewhat tendinous.

_Relations._—Inferior to the hyoid apparatus and superior larynx.

_Action._—When the larynx is fixed, acting alone deflects the tongue laterally; acting with its fellow, depresses the tongue. If the base of the tongue is fixed the two pull the larynx forward. Hence muscles of deglutition.

=Depressor-glossus.= _Location._—Superior to the basi-hyal.

_Origin._—From the under portion of the basi-hyal.

_Insertion._—To under part of the glosso-hyal.

_Shape._—Small, short.

_Relations._—Superiorly with the basi-hyal and glosso-hyal bones.

_Action._—Depresses the tip of the tongue and elevates the base.

=Cerato-glossus.= _Location._—On the upper portion of the cornu of the hyoid.

_Origin._—One-half of the surface of the first basi-branchial.

_Insertion._—To the upper side of the shaft of the cerato-branchial element of the hyoid apparatus.

_Shape._—A small muscular fasciculus.

_Relations._—Supero-laterally to the cerato-branchial element.

_Action._—Elevates the cornua of the hyoid arches and presses them against the skull.

=Hyoideus Transversus= (Fig. 9, No. 9 and 10). _Location._—Envelops the spur process of the euro-hyal.

_Origin and Insertion._—It extends from the inner side of one cornu to the spur process.

_Shape._—Thin, flat.

_Relations._—Posterior to the euro-hyal, which it envelops, and between the cornua of the os hyoides.

_Action._—Approximates the cornua of the os hyoides.

The Cervical Muscles

Complexus Rectus capitis anticus minor Flexor capitis inferior Rectus capitis posticus major Biventer cervicis Longus colli posticus Obliquus colli Longus colli anterior Rectus capitis lateralis Trachelo-mastoideus Interspinales Interarticulares Obliquo-transversales Intertransversales Scalenus medius

=Complexus= (Fig. 19, No. 5). _Location._—Supero-lateral portion of the neck.

_Origin._—By three tendinous slips from the antero-lateral portion of the transverse process of the fourth, the fifth, and the sixth cervical vertebræ.

_Insertion._—The muscular fibers pass around the neck and meet their fellows in the median line in a fascia formation. The thin tendinous sheet inserts into the occiput just above the occipital ridge.

_Shape._—From point of origin this muscle expands into a broad sheet.

_Relations._—It overlies the muscles of the occipital region.

_Action._—It extends the head.

=Rectus Capitis Anticus Minor= (Fig. 19, No. 8). (Synonym.—Rectus capitis ventralis minor.)

_Location._—Infero-lateral portion of the neck.

_Origin._—From the apices of the hyapophyses of the second, the third, and the fourth cervical vertebræ.

_Insertion._—To the occiput just below the complexus.

_Shape._—A long and rather thick fasciculus.

_Relations._—Externally with the skin. The tendinous slips of origin pass between the flexor capitis inferior and longus colli anterior.

_Action._—Extends the head.

=Flexor Capitis Inferior= (Fig. 19, No. 7). _Location._—Antero-inferior part of the neck.

_Origin._—From the apices of the hyapophyses of the second, the third, and the fourth cervical vertebræ.

_Insertion._—To the triangular area on the basi-temporal of the base of the cranium.

_Shape._—At first tendinous, becomes somewhat fleshy as it passes forward.

[Illustration:

FIG. 19.—Muscles of the head and neck. 1, Masseter muscle. 2, Infraorbital sinus. 3, Biventer maxilla. 4, Temporalis. 5, Complexus. 6, Rectus capitis posticus major. 7, Flexor capitis inferior. 8, Rectus capitis anticus minor. 9, Biventer cervicis. 10, Longus colli posticus. 11, Obliquus colli. 12, Intertransversales. 13, Longus colli anterior. 14, Lateral temporo-maxillary ligament. 15, Lateral ligament of the jaw. 16, Trachelo-mastoideus. 17, Rectus capitis lateralis. 18, Scalenus medius. 19, Rhomboideus. 20, Trapezius. 21, Location of scapula. 22, Supraspinatus. 23, Teres et Infraspinatus. ]

_Relations._—Antero-inferior portion of the neck close to the rectus capitis anticus minor.

_Action._—Flexes the head upon the neck.

=Rectus Capitis Posticus Major= (Fig. 19, No. 6). (Synonym.—Rectus capitis dorsalis major.)

_Location._—Supero-lateral area on the anterior portion of the neck.

_Origin._—From the median anterior aspect of the second cervical vertebra, and the supero-anterior border of the neural canal.

_Insertion._—To the crescent-shaped area at the back of the skull.

_Shape._—Short, thick, fleshy bundle.

_Relations._—Superiorly with the complexus; inferiorly with the trachelo-mastoideus and the vertebræ.

_Action._—Singly, pulls the head to one side; acting with its fellow, extends the head.

=Biventer Cervicis= (Fig. 19, No. 9). _Location._—Occupies the superior part of the neck.

_Origin._—From the side of the neural spine of the first dorsal vertebra, and from the adjacent tendon of the longus colli posticus.

_Insertion._—To the occiput.

_Shape._—Tendinous in the middle with a more or less spindle-shaped belly at each end.

_Relations._—Superior to the longus colli posticus. It lies next to the skin.

_Action._—Extends the head on the neck and elevates the neck.

=Longus Colli Posticus= (Fig. 19, No. 10). (Synonym.—Longus colli dorsalis.)

_Location._—Occupies the superior part of the neck.

_Origin._—From the marginal edges of the summits of the neural spines of the first two dorsal vertebræ.

_Insertion._—To the transverse process of the axis, and superior part of the cervical vertebræ.

_Shape._—A long, somewhat narrow, flattened muscle, the inferior portion of which is divided into five or six fasciculi.

_Relations._—Superiorly with the biventer cervicis and inferiorly with the vertebræ.

_Action._—Raises the neck upward.

=Obliquus Colli= (Fig. 19, No. 11). _Location._—On the lateral side of the neck.

_Origin and Insertion._—The first of the seven fasciculi originates from the diapophysis of the eleventh cervical vertebra, winds obliquely over the tenth, and is inserted into the posterior margin of the postzygapophysis of the ninth vertebra.