Chapter V: Part II: 1, The os occipitale (1, dorsal; 2, two lateral; 3, ventral (4)

_Insertion._—The fibers, passing downward, then downward and outward, terminate in a small tendon at the lower third of the tibia. This tendon bifurcates just above the tibial condyles at the outer part of the limb, the shorter and stronger attaches to the fibrous fascia covering the tibial cartilage, the other merging with the tendon of the flexor perforatus medius primus pedis about 1 centimeter below the hypotarsus of the tarso-metatarsus.

_Relations._—Covers over all the muscles of the anterior tibial region.

_Shape._—A broad muscular sheet.

_Action._—Assists the flexor perforatus medius primus pedis.

=Tibialis Anticus= (Fig. 24, No. 22). _Location._—In the anterior tibial region.

_Origin._—The muscular belly may be easily divided into two parts. The inner head extends from the head of the tibia immediately beneath the peroneus longus. The outer head arises by a strong tendon from a depression on the antero-inferior ridge of the outer condyle of the femur.

_Insertion._—The tendon passing through the fibrous ligamentous loop just above the tibial condyles, inserts to a tubercle on the shaft just below the head of the tarso-metatarsus.

_Shape._—Large, fusiform.

_Relations._—Beneath the peroneus longus.

_Action._—Flexes the metatarsus upon the tibia.

=Extensor Longus Digitorum= (Fig. 25, No. _G_, 6). _Location._—Anterior tibial region.

_Origin._—From the inferior portion of the crest and a portion of the shaft of the fibula.

_Insertion._—It becomes tendinous at the lower third of the bone, passing under the bony ridge just above the condyle in front, and over the ankle-joint. It is bound down by firm fascia, and at the trochlea of the basal toe joints, divides into three small tendinous slips. These pass over the superior part of the second, the third, and the fourth toes, bifurcating in their course, and are inserted to the distal ones.

_Shape._—Long, penniform, with a long, slender tendon.

_Relations._—Immediately below the tibialis anticus.

_Action._—Extends the digits as their long extensor.

=Extensor Hallucis Brevis= (Fig. 25, No. _G_, 4). _Location._—The anterior metatarsal region, along the antero-internal edge.

_Origin._—From just below the summit of the antero-internal part of the head of the tarso-metatarsus, and from the adjacent shaft below, and from the tendon of the tibialis anticus.

_Insertion._—Into the process at the superior part of the bone of the bony claw of the hallux.

_Shape._—Slender, thin in diameter, with a long, slender tendon.

_Relations._—Superiorly, with the antero-internal edge of the metatarsus and interiorly, its tendon with the top of the hallux.

_Action._—Extends the hallux.

=Extensor Brevis Digitorum.= _Location._—On the anterior surface of the metatarsus.

FIG. 25.—Inner layer of muscles of the thigh of a hen. Outside view.

_A._ Pad of fibrocartilage or meniscus of femoro-tibial articulation.
1, Inner semi-lunar fibrocartilage. 2, External semi-lunar
cartilage. 3, Anterior border.

_B._ Tarsal meniscus or pad of fibrocartilage.

_C._ Articular surface of the tarsal joint. 1, Posterior ligamentum
cruciatum genu. 2, Femoral tendinous insertion of tibialis anticus.
3, Ligamentum tibio-fibulare. 4, Ligamentum interosseum. 5,
Ligamentum transversum of the meniscus. 6, Anterior ligamentum
cruciatum genu.

_D._ 1, Tibia. 2, Fibula. 3, Femur. 4, External ligamentum laterale
genu.

_E._ Inferior surface of the tail of a hen. 1, Infracoccygis. 2,
Lateralis coccygis.

_F._ Outside pelvic view. 1, Obturator ligament. 2, Tendon of the
obturator internus. 3, Ligamentum oblongum. 4, Ligamentum capsulare.
5, Gemellus.

_G._ Outside view of leg of a cock. 1, Soleus. 2, Flexor longus
hallucis. 3, Flexor perforans digitorum profundus. 4, Extensor
brevis hallucis. 5, Extensor brevis annularis. 6, Extensor longus
digitorum. 7, Tendon of the tibialis posticus.

_H._ 1, Transversalis abdominalis. 2, Cotyloid cavity.
]

_Origin._—By a small fleshy belly to the anterior part of the proximal end of the metatarsus.

_Insertion._—It becomes tendinous about the middle third of the metatarsus. Extending down the anterior face of the metatarsus it is inserted to the inner tubercle of the base of the first phalanx of the outer or fourth toe.

_Shape._—Long, slender.

_Relations._—Posteriorly with the metatarsus.

_Action._—Pulls the fourth toe upward and inward.

=Flexor Hallucis Brevis.= _Location._—Postero-internal side of the metatarsus.

_Origin._—Side and lower margin of the inner aspect of the hypotarsus of the tarso-metatarsus and from the shaft of this bone immediately below it.

_Insertion._—Winds round inner side of basal joint of the hallux and is inserted on its under side.

_Shape._—Small flat muscle gradually tapering into a tendon.

_Relations._—Posteriorly with the metatarsus.

_Action._—To flex the hallux.

=Extensor Annularis Brevis.= _Location._—On postero-external side of metatarsus.

_Origin._—External aspect of the hypotarsus and the shaft below.

_Insertion._—Supero-external part of the basal phalanx of the fourth toe.

_Shape._—Small flat muscle.

_Relations._—Posteriorly with the metatarsus.

_Action._—Extensor of the fourth toe.

=Tibialis Posticus= (Fig. 24, No. 23). _Location._—In the posterior tibial region.

_Origin._—From the whole shaft of the fibula below the insertion of the biceps flexor cruris, and from the shaft of the tibia a short distance below this insertion. Also from the interosseous membrane, and the adjacent surface of the tibial shaft.

_Insertion._—Passing in front of the external malleolus, crossing the ankle-joint, finally inserted into the outer edge of the summit of the tarso-metatarsal bone.

_Shape._—Long, subcylindrical.

_Relations._—Medially, with the flexor perforans digitorum pedis; superiorly, with the postero-external portion of the tibia.

_Action._—Extends the metatarsus upon the tibia.

=Flexor Perforatus Indicis Secundus Pedis= (Fig. 17, No. 5). _Location._—The posterior tibial region.

_Origin._—From the external surface of the outer condyle of the femur, just below the head of the gastrocnemius.

_Insertion._—Passing in an oblique manner along posterior to the tibia, extends through the superficial part of the tibial cartilage to the outer side of the leg; then crossing the tibio-tarsal joint, it passes through a special canal of the hypotarsus, down the back of the tarso-metatarsus, under the annular ligament of the sole of the foot and a cartilaginous structure below this ligament, over the trochlea, and is inserted to the middle shaft of the second phalanx of the second toe.

_Shape._—Thin, flat, broadly spindle-shaped.

_Relations._—Posteriorly, with the flexor perforatus medius secundus pedis, and anteriorly, with the flexor perforatus annularis primus pedis.

_Action._—Flexes the toes.

=Flexor Longus Hallucis= (Fig. 17, No. 7; Fig. 25, No. 2). _Location._—The posterior tibial region.

_Origin._—By two tendinous heads: one from the posterior part of the femur, just below the two condyles; the other from the outer part of the external condyle of the femur. The deep flexor passes between these two heads.

_Insertion._—Becoming tendinous at the lower third of the leg, passes beneath the superficial flexors in a special canal on the outer side of the tibial cartilage, and extends through the large canal of the hypotarsus (Fig. 12, No. _F_, 5) next to the shaft, then down to the apex of the accessory metacarpal bone. It is inserted to the tubercle on the inferior proximal end of the ungual phalanx.

_Shape._—Large, fusiform.

_Relations._—With the exterior of the deep flexors.

_Action._—Flexes the hallux as its long flexor.

=Flexor Perforatus Annularis Primus Pedis= (Fig. 17, Nos. _D_, 8 and _C_, 6). _Location._—The posterior tibial region.

_Origin._—From the inner side of the belly of the flexor longus hallucis.

_Insertion._—Becoming tendinous at the lower third of the tibia, passes a little to the outer side and through the tibial cartilage, then over the ankle-joint and through the hypotarsal canal (Fig. 12, No. 5) to the under side of the outer toe, where it forms a sheath through which the deep flexors extend. It gives off on either side a tendinous slip which attaches to the basal phalanx.

_Shape._—Long, slender, compressed laterally.

_Relations._—Internally, with the flexor perforatus indicis secundus pedis, and externally, with the flexor longus hallucis.

_Action._—Flexes the toes as their long flexor. A second flexor of the outer toe.

=Flexor Perforatus Medius Secundus Pedis= (Fig. 17, No. 9). _Location._—The posterior tibial region.

_Origin._—From a strong fascia that merges with the knee-joint, and by a tendon from the external condyle of the femur in common with the tendon of the flexor perforatus indicis secundus pedis.

_Insertion._—Continued as a flattened tendon extending from the lower third of the leg, passing obliquely through the tibial cartilage and then through the interno-posterior canal of the hypotarsus, (Fig. 12, No. _F_, 5) inserted to the second joint of the middle toe.

_Shape._—Long, fusiform.

_Relations._—With the shaft of the fibula, which it covers.

_Action._—Flexes the middle toe.

=Flexor Perforatus Medius Primus Pedis= (Fig. 17, No. 2). _Location._—Posterior tibial region.

_Origin._—From the inner side of the muscular portion of the flexor perforatus annularis primus pedis.

_Insertion._—Terminating in a flattened tendon, passes through the tibial cartilage and hypotarsus, and then extends along the shaft of the basal joint of the third toe, and, dividing into two slips, inserts to either side of its shaft.

_Shape._—Long, rather small.

_Relations._—With the flexor perforatus annularis primus pedis on the inner side.

_Action._—Flexes the third toe.

=Flexor Perforatus Indicis Primus Pedis= (Fig. 17, No. 4). _Location._—The posterior tibial region.

_Origin._—From a thin, broad tendon, on the external condyle of the femur, in common with the flexor perforatus medius secundus pedis.

_Insertion._—Becoming tendinous, passes through the tibial cartilage and the hypotarsus of the metatarsus (Fig. 16, _A_) and inserts to the sides of the basal joint of the second toe.

_Shape._—Long, slender, fusiform; somewhat flattened laterally.

_Relations._—With the flexor perforatus medius secundis pedis, posteriorly.

_Action._—A flexor of the toes.

=Flexor Perforans Digitorum Profundus= (Fig. 24, No. 24 and Fig. 25, No. _G_, 3). _Location._—The posterior tibial region.

_Origin._—From the posterior part of the external condyle of the femur, from the posterior part of the tibia just below the summit, and from a point near the origin of the soleus.

_Insertion._—Its heavy flattened tendon passes through the tibial cartilage, this tendon dividing, the branches pass along the under side of the toes, perforating the outer tendons and become inserted to the proximal tubercle at the base of the under side of the ungual phalanxes of the second, third, and fourth toes.

_Shape._—Long, fleshy, with a long tendon.

_Relations._—Closely with the tibial bone; the deepest of all the flexors.

_Action._—Flexes the digits.

THE MUSCLES OF THE EYE

Orbicularis palpebrarum
Depressor palpebræ inferioris
Pyramidalis nictitans
Obliquus inferior
Rectus inferior
Levator palpebræ superioris
Quadratus nictitans
Obliquus superior
Rectus superior
Rectus externus
Rectus internus

=Orbicularis Palpebrarum= (Fig. 7, No. 30). (Synonym.—Orbicularis oculi.)

_Location._—Upon the lacrimal and maxillary bones.

_Origin._—From the lacrimal and maxillary bones and the ciliary margin.

_Insertion._—To the lower free edge of the tarsal cartilage.

_Shape._—Thin, delicate layer of fibers.

_Relations._—Externally, with the skin; internally, with the lacrimal and the maxillary bones.

_Action._—Aids in closing the eye.

=Levator Palpebræ Superioris= (Fig. 7, No. 24). _Location._—Along the superior roof of the orbit.

_Origin._—Along a longitudinal line found near the middle of the roof of the orbit.

_Insertion._—To the ciliary margin of the upper lid, near the outer canthus.

_Shape._—Thin, delicate layer.

_Relations._—Superiorly, with the bony wall, and inferiorly, with the eyeball.

_Action._—Raises the superior eyelid.

=Depressor Palpebræ Inferioris= (Fig. 7, No. 29). (Synonym.—Malaris.)

_Location._—Along the inferior border of the eye.

_Origin._—From the inferior border of the interorbital foramen.

_Insertion._—To the lower lid.

_Shape._—Thin, flat, delicate.

_Relations._—Superiorly, with the eyeball; inferiorly, with the inferior orbital wall.

_Action._—Pulls the lower lid down.

=Quadratus Nictitans= (Fig. 26, No. _B_, 7). _Location._—Above the eyeball along the inferior border of the upper wall of the orbit.

_Origin._—From the sclerotic from the upper part of the ball.

_Insertion._—To the upper part of the sheath of the optic nerve near the optic foramen.

_Shape._—Broad, thin, quadrate.

_Relations._—Inferiorly, with the eyeball; superiorly, with the orbital wall, with the superior oblique, and with the superior rectus.

_Action._—Aids in pulling the nictitating membrane obliquely outward and downward over the forepart of the eyeball.

=Pyramidalis Nictitans= (Fig. 26, No. _B_, 8). _Location._—Inferoposteriorly to the eyeball.

_Origin._—From the lower nasal side of the eyeball.

_Insertion._—The fibers converge toward the upper part of the optic nerve, into a tendon which passes through a pulley at the free margin of the quadratus. Inserts to the lower part of the margin of the third eyelid, the nictitans.

_Shape._—Pyramidal; of thin layers of fibers.

_Relations._—Internally, with the bony orbital wall; externally, with the eyeball.

_Action._—Aids the quadratus nictitans.

=Obliquus Superior= (Fig. 26, No. _B_, 5). (Synonym.—Obliquus dorsalis.)

_Location._—Superior to the eyeball.

FIG. 26.—Structures of the eye and nasal passage.

_A._ 1, The anterior turbinated bone. 2, The posterior turbinated
bones. 3, Orbital gland. 4, Ophthalmic division of the fifth pair of
cranial nerves. 5, Section through the cerebrum. 6, Section through
the skull showing the air spaces. 7, Section through the comb. 8,
Anterior portion of the upper beak. 9, Edge of the hard palate.

_B._ The intrinsic muscles of the eyeball. 1, Superior rectus. 2,
Internal rectus. 3, Inferior rectus. 4, External rectus. 5, Superior
oblique. 6, Inferior oblique. 7, Quadratus. 8, Pyramidalis. 9, Optic
nerve. 10, Edge of membrana nictitans.

_C._ Posterior part of the eye showing at the inferior portion of the
ball the pyramidalis muscle at 1, and at 2, the quadratus. 3, Optic
nerve.

_D._ Inner view of the posterior part of the vitreous chamber. 1,
Sclerotic coat. 2, Choroid coat. 3, Retina. 4, Pecten.

_E._ Longitudinal section through the eye of a hen. 1, Cornea. 2,
Anterior chamber. 3, Scleral ring. 4, Crystalline lense. 5, Iris. 6,
Retina. 7, Sclerotic. 8, Choroid. 9, Pecten. 10, Optic nerve. 11,
Vitreous chamber.

_F._ An edge view of the crystalline lense of a hen showing it to be
asymmetrical biconvex. 1, The anterior side. 2, The posterior side.

_G._ The upper section through the anterior portion of the anterior
turbinated bone showing one complete circle and the lower a section
through the middle turbinated showing one and one-half turns.
]

_Origin._—From the orbital septum just back of the inner canthus, the fibers passing backward and forward.

_Insertion._—Into the sclera, anterior to the sclerotic plates.

_Shape._—Small, thin, fan-shaped.

_Relations._—With the eyeball, superiorly; at its extremities with the superior rectus, interiorly.

_Action._—Rotates the eyeball.

=Obliquus Inferior= (Fig. 26, No. _B_, 6). (Synonym.—Obliquus ventralis.)

_Location._—Inferior to the eyeball.

_Origin._—From the interorbital septum near the inner canthus of the eye.

_Insertion._—By a broad expansion to the inferior portion of the eyeball.

_Shape._—Tendinous at its insertions; fan-shaped as it passes downward and outward.

_Relations._—Internally, with the eyeball; and externally, with the bony orbital wall, with the inferior rectus muscle, inferiorly.

_Action._—Aids in rotating the eye; opposes the obliquus superior.

=Rectus Superior= (Fig. 26, No. _B_, 1). (Synonym.—Rectus dorsalis.)

_Location._—Superior to the eyeball.

_Origin._—Along the supero-posterior border of the optic foramen.

_Insertion._—To the sclera just within the margin of the bony circle of the eye.

_Shape._—Flat, thin.

_Relations._—Internally, with the obliquus superior; superiorly, with the bony wall of the orbit.

_Action._—To pull the eyeball upward.

=Rectus Inferior= (Fig. 26, No. _B_, 3). (Synonym.—Rectus ventralis.)

_Location._—Inferior to the eyeball.

_Origin._—From the inferior border of the optic foramen.

_Insertion._—To the lower portion of the eyeball within the margin of the bony circle of the eye.

_Shape._—Thin, fan-shaped.

_Relations._—Superiorly, with the eyeball; inferiorly, with the bony wall of the orbit.

_Action._—Pulls the eyeball downward.

=Rectus Externus= (Fig. 26, No. _B_, 4). (Synonym.—Rectus lateralis.)

_Location._—External to the eyeball.

_Origin._—By two heads infero-laterally to the optic foramen.

_Insertion._—To the postero-external side of the eyeball.

_Shape._—Short, fan-shaped.

_Relations._—Internally, with the eyeball; externally, with the bony wall of the orbit.

_Action._—Pulls the eyeball outward.

=Rectus Internus= (Fig. 26, No. _B_, 2). (Synonym.—Rectus medialis.)

_Location._—Inner side of the eyeball.

_Origin._—From the supero-anterior border of the optic foramen.

_Insertion._—To the sclera on the anterior portion of the eyeball.

_Shape._—Thin, fan-shaped.

_Relations._—Internally, with the eyeball and with the pyramidalis; externally, with the bony wall of the orbit.

_Action._—Pulls the eyeball inward.

THE MUSCLES OF THE EAR

Circumconcha
Tensor tympani

=Circumconcha= (Fig. 7, No. 32). _Location._—Surrounds the external ear.

_Origin and Insertion._—The circumconcha, surrounding the periphery of the ear, is adherent to the skull and loosely to the skin, and is attached to the outer terminus of the supra-occipital crest.

_Relations._—Internally, with the skull; externally, with the skin.

_Action._—Relaxes the tympanum.

=Tensor Tympani= (Fig. 7, No. 31). _Location._—External to the quadrate and to the external auditory meatus.

_Origin and Insertion._—From the surface of the quadrate and the inner end of the quadrato-jugal to the inner surface of the tympanum.

_Shape._—A few fibers.

_Relations._—Internally, with the quadrate and the quadrato-jugal; externally, the integumental duplicature.

_Action._—Tenses the tympanum.

FUNCTIONS OF MUSCLES

To cause the feathers on the top of the head to lie flat:
Dermo-frontalis.
To raise the feathers along the superior part of the neck and along the
dorsal region:
Dermo-dorsalis.

To tense the patagial region:
Dermo-tensor patagii,
Dermo-temporalis.
To cause the feathers to lie close to the body:
Dermo-humeralis,
Dermo-pectoralis.
To tense the lateral cervical integument:
Dermo-temporalis.
To support the lingual apparatus and superior larynx:
Platysma myoides.
To manipulate the feathers and skin of the inferior part of the neck:
Cleido-trachealis.
To control the skin in the shoulder region:
Dermo-spinalis.
To cause the feathers of the back to lie close to the skin:
Dermo-iliacus.
To depress the humeral region:
Dermo-ulnaris.
To close the jaw:
Temporalis,
Pterygoideus internus,
Pterygoideus externus,
Masseter.
To open the jaw:
Biventer maxilla,
Entotympanic.
To raise the trachea and hyoid apparatus:
Digastricus.
To elevate the tongue:
Mylo-hyoideus.
To pull the tongue to one side:
Singly[5]—
Cerato-hyoideus,
Stylo-hyoideus.
Alone when the larynx is fixed—
Sterno-hyoideus.
Those which protrude the tongue from the mouth:
Together—
Cerato-hyoideus,
Genio-hyoideus.
To aid in deglutition:
When the base of the tongue is fixed—
Sterno-hyoideus.
To depress the tongue:
Together—
Sterno-hyoideus.

To depress the tip of the tongue and elevate the base:
Depressor glottis.
To elevate the hyoid arches:
Cerato-glossus.
To extend the head:
Complexus,
Rectus capitis anticus minor.
To flex the head upon the neck:
Flexor capitis inferior.
To extend the head on the neck and elevate the neck:
Biventer cervicis.
To raise the neck upward:
Longus colli posticus.
To flex each vertebra on the preceding or succeeding laterally:
Obliquus colli,
Intertransversales.
To pull the neck downward:
Longus colli anterior.
To pull the head downward:
Together—
Rectus capitis lateralis,
Trachelo-mastoideus.
To pull the head downward and to one side:
Singly—
Rectus capitis lateralis,
Trachelo-mastoideus.
To approximate the spinous processes of the vertebræ:
Interspinales.
To approximate the vertebræ in a supero-lateral direction:
Interarticulares.
To flex the vertebræ supero-laterally:
Obliquo-transversales.
To extend the neck:
Together when the first rib is fixed—
Scalenus medius.
To close the glottis:
Constrictor glottidis.
To open the glottis:
Thyreo-arytenoideus.
To approximate the tracheal rings:
Tracheo-lateralis.
To tense the inferior larynx:
Broncho-trachealis posticus,
Broncho-trachealis anticus,
Broncho-trachealis brevis,
Bronchialis posticus,
Bronchialis anticus.

To relax the inferior larynx:
Sterno-trachealis.
To aid in respiration:
When the first rib is fixed—
Intercostales.
When wing is fixed—
Latissimus dorsi,
Dermo-cleido dorsalis.
When the scapula is fixed—
Serratus magnus anticus,
Serratus parvus anticus,
Thoraco-scapularis,
Levatores costarum,
Appendico-costales,
Triangularis sterni.
To flex the shoulder-joint:
Latissimus dorsi.
To elevate the humerus:
Latissimus dorsi.
To draw the scapula forward:
Trapezius,
Rhomboideus.
To close the wing:
Teres et infraspinatus.
To extend the humerus:
Coraco-humeralis,
Scapulo-humeralis.
To pull the humerus upward and backward:
When the scapula is fixed—
Supraspinatus.
To pull the coracoid outward:
Subclavius.
To depress the wing:
Coraco-brachialis.
To depress the scapula:
When the ribs are fixed—
Thoraco-scapularis.
To rotate the humerus:
Subscapularis.
To flex the forearm:
Pronator brevis,
Biceps,
Brachialis anticus,
Anconeus,
Tensor patagii longus,
Tensor patagii brevis.
To extend the arm:
Deltoid.

To extend the antibrachial region:
Triceps.
To raise and to draw the hand forward:
Extensor metacarpi radialis longior.
To extend the digit:
Extensor indicis longus,
Extensor digitorum communis,
Extensor proprius pollicis,
Interosseous dorsalis.
To supinate the radial region:
Supinator brevis.
To flex the hand:
Flexor metacarpi radialis.
To pronate the forearm:
Pronator brevis,
Pronator longus.
To extend the hand on the forearm:
Extensor ossis metacarpi pollicis.
To flex the digit:
Flexor minimi digiti,
Flexor digitorum sublimis,
Flexor brevis pollicis,
Flexor digitorum profundus,
Interosseous palmaris.
To flex the hand upon the forearm:
Flexor carpi ulnaris,
Flexor carpi ulnaris brevior.
To rotate the hand toward the body:
Flexor carpi ulnaris brevior.
To abduct the digits:
Abductor minimi digiti.
To flex the metacarpus:
Flexor metacarpi brevis.
To extend the leg:
Sartorius.
To adduct the thigh:
Sartorius,
Adductor longus,
Adductor magnus.
To abduct the thigh:
Gluteus primus,
Gluteus medius,
Gluteus minimus.
To pull the thigh forward:
Gluteus minimus,
Gluteus medius.
To extend the leg upon the thigh:
Extensor femoris,

Vastus internus.
To extend the leg upon the knee:
Vastus internus.
To flex the leg upon the thigh:
Biceps flexor cruris,
Semitendinosus,
Semitendinosus accessorius,
Semimembranosus.
To pull the tail down and to one side:
Femoro-caudal.
To pull the head of the femur backward:
Obturator externus.
To act as a posterior stay to the head of the femur:
Obturator internus.
To pull the pelvis forward and to steady it on the head of the femur:
Gemellus,
Obturator internus,
Obturator externus.
To extend the metatarsus on the tibia:
Gastrocnemius,
Soleus,
Tibialis posticus.
To flex the toes:
Peroneus longus,
Flexor perforatus medius primus pedis,
Flexor perforatus indicis secundus pedis,
Flexor perforatus medius secundus pedis,
Flexor perforatus indicis primus pedis,
Flexor perforans digitorum profundus,
Flexor longus hallucis,
Flexor perforatus annularis primus pedis.
To flex the metatarsus on the tibia:
Tibialis anticus.
To extend the toes:
Extensor longus digitorum,
Extensor hallucis brevis.
To flex the back laterally and to aid in raising the body.
Sacro-lumbalis,
Longissimus dorsi.
To elevate the tail:
Levator coccygis,
Levator caudæ.
To depress the tail:
Depressor caudæ,
Infracoccygis.
Together—
Depressor coccygis,
Lateralis caudæ.

To pull the tail downward and to one side:
Singly—
Lateralis coccygis.
Depressor coccygis,
Lateralis caudæ.
To close the eyelids:
Orbicularis palpebrarum.
To raise the superior eyelid:
Levator palpebræ superioris.
To pull the lower eyelid downward:
Depressor palpebræ inferioris.
To pull the membrana nictitans over the eyeball:
Quadratus nictitans,
Pyramidalis nictitans.
To rotate the eyeball:
Obliquus superior,
Obliquus inferior.
To pull the eyeball upward:
Rectus superior.
To pull the eyeball downward:
Rectus inferior.
To pull the eyeball outward:
Rectus externus.
To pull the eyeball inward:
Rectus internus.
To tense the ear drum:
Tensor tympani.
To relax the ear drum:
Circumconcha.
To depress the humerus:
Pectoralis major.
To raise the humerus:
Pectoralis secundus,
Pectoralis tertius.

Footnote 5:

Muscles are arranged in pairs. Singly means one muscle acting alone,
_i.e._, without its fellow; together means acting both at the same
time.

SPLANCHNOLOGY

=The Digestive Apparatus.=—This apparatus, apparatus digestorius, consists of the organs directly concerned in the reception of food, in its passage through the body, and in the expulsion of the unabsorbed portion. For convenience, these organs are grouped as follows: the alimentary canal and the accessory organs.

The alimentary canal is a tube which extends from the mouth to the anus. It has a complete lining of mucous membrane, external to which is an almost continuous muscular coat. The abdominal portion of the tube is largely covered with a serous membrane, the visceral peritoneum. The canal consists of the following consecutive segments: mouth, pharynx, first portion of the esophagus, crop, second portion of the esophagus, proventriculus, gizzard, small intestine, large intestine, and cloaca.

The accessory organs are beak, tongue, salivary glands, liver, and pancreas.

=The Mouth= (Fig. 27).—The distinctive character of the mouth of the fowl consists, in the absence of lips and teeth and instead of jaw bones of other animals, of a _beak_. The edge of the beak is covered by a horn-like gum. The shape of the beak differs in the various classes of birds. In the chicken the beak is short, strong, thick, and pointed; in palmipeds it is flattened. The upper mandible extends out over the lower mandible. The outer portion of the upper and the lower beaks is covered by a horny sheath. There is no velum, and the mouth cavity is extended rather continuously into the pharynx (Fig. 27, No. 4). The posterior cross bar of the hard palate (Fig. 27, No. 5), which possesses a row of filiform papillæ projecting backward, marks the upper boundary line of the mouth; while the posterior end of the tongue (Fig. 27, No. 6), likewise with a row of filiform papillæ, marks its lower boundary line.

_Parts of the Mouth._—The mouth of fowls is divided into an upper and a lower half. The upper half is divided into an anterior and a posterior part.

The anterior part extends from the anterior tip of the beak to the posterior nares. It is further divided into an outer hard part and an inner soft part. The outer part is covered by epithelium which may be considered as a continuation from the upper outer portion of the beak. A portion of this is cornified. The inner part is covered by a mucous membrane containing mucous glands, nerves, and blood-vessels.

In the posterior part of the upper half of the mouth, are situated the posterior nares (Fig. 27, No. 10) which appear as a longitudinal slit in the center of the hard palate. There is also found in this part a furrow which contains the opening of the Eustachian tubes, or tubæ auditivæ. There are also two ridges near the same posterior part in which are red and white papillæ, which may appear in rows, and which contain mucous glands.

FIG. 27.—Mouth and pharynx of a cock laid open. 1, Eye. 2, Edge of
beak covered with a horn-like gum. 3, Tongue. 4, Pharynx. 5,
Posterior cross bar of hard palate. 6, Posterior end of tongue. 7,
Anterior end of esophagus. 8, Phrenum. 9, Palatal papillaries. 10,
Posterior nares.
]

The lower half of the mouth lies between the lower jaw bones and the walls of the mouth cavity. The tongue is attached here by means of the phrenum (Fig. 27, No. 8). This half of the mouth forms a pocket-like structure which aids in taking up the food.

The mouth cavity is lined with stratified squamous epithelium, continuous with that of the pharynx and the esophagus. Taste buds are located in the mucous membrane of the mouth.

FIG. 28.—Various anatomical parts of the fowl.

_C._ A section through the nasal region of the fowl. 1, Nasal passages
showing the turbinated bones dividing the nasal passage into the
superior, middle and inferior meati. 2, The infraorbital sinus. 3,
The hard palate.

_D._ Herbst’s touch corpuscle from the beak of a quail.

_E._ A vertical section through the ductus cochlearis of a pigeon. 1,
A blood-vessel. 2, The periosteum. 3, The bony structure. 4, The
vascular integument. 5. The scala vestibuli. 6, The inner hyaline
cylindrical cells. 7, The membrana tectoria. 8, The papilla acustica
basilaris. 9, The membrana basilaris. 10, The scala tympani. 11, The
ganglion of the cochlear nerve in the ramus basilaris. 12, The
periosteum (Gadow).

_F._ A corpuscle of the soft papilla of a duck’s tongue.

_J._ A transverse section through a feather papilla. 1, The pulp. 2,
The malpighian layer. 3, The corium. 4, The stratum corneum of the
papilla. 5, The malpighian cell group of the main shaft. 6, The
horny sheath.
]

In many water fowls, as geese and ducks, the gum edge of the mandible has grooves extending crosswise, in which are numerous terminals of the trigeminus nerve arranged as taste organs (Fig. 29, _G_ and Fig. 28, _D_ and _F_). In many birds of prey and in water birds, _e.g._, the goose and the duck, there is found at the base of the beak, a very thin, nervous or sensitive skin, waxy in appearance, called the ceroma.

FIG. 29.—Various anatomical parts of the fowl.

_A._ 1, The superior semicircular canal. 2, The vestibular nerve. 3,
The meatus auditorius internus—the entrance of the auditory nerve.
4, The entrance of the cochlear nerve. 5, Posterior semicircular
canal. 6, The ampulla.

_B._ Side papilla of the tongue. 1 and 2, Papillæ showing a fibrous
central core supporting blood-vessels and nerves. 3, The basement
membrane consisting of connective tissue.

_G._ Herbst’s corpuscle of the tongue of a duck, showing the capsule,
lamella and around the nerve zone, numerous round bodies arranged in
two rows.

_H._ From the cristæ acoustica of the ampulla of the dove. A, A
vertical section with isolated fiber cells. 1 and 2, The nerve
fibers. 3, The hair cells.

_I._ A longitudinal section through a feather papilla showing a young
feather. 1, The developing feather. 2, The horny sheath. 3, The
epithelium. 4, Stratum corneum. 5, Stratum malpighi. 6, Corium. 7,
Malpighian cell group of the follicle.
]

_The Hard Palate._—The hard palate, palatum durum, forming the roof of the mouth has for its boundaries the beak anteriorly, the mandibular arches laterally, and the pharynx posteriorly. It has four or five transverse bars, projecting posteriorly from each of which is a row of filiform papillæ (Figs. 27 and 29).

FIG. 30.—A section through the wall of the crop of a hen. 1, The outer
muscular layer showing longitudinal fibers. 2, The inner muscular
layer showing the sectioned ends of the bundles of muscle fibers. 3,
Stratified squamous epithelium. 4, The outer surface or lumen of a
fold. 5, The stroma, muscularis mucosa, and submucosa.
]

The _beak_ (Fig. 4, No. 1) with little if any aid from the tongue, is the prehensile organ.

=The Tongue= (Fig. 27, No. 3). _Location._—The tongue (lingua) of the fowl is situated in the floor of the mouth between the rami of the lower mandible, and is slung to the cranium by the cerato-branchial element of the os hyoideum (Fig. 18, No. 2).

_Shape._—The tongue, is pointed in front and wide behind, shaped like an Indian arrow-head, and is supported by the bony and cartilaginous hyoid apparatus (Fig. 9, _A_).

FIG. 31.—The visceral organs of the hen. 1, Tongue. 2, Larynx. 3,
Glottis. 4, First portion of the esophagus. 5, Crop. 6, Second
portion of the esophagus. 7, Proventriculus. 8, Duodenum. 9, Free or
floating portion of the small intestine. 10, Mesentery supporting
the free portion of the small intestine. 11, Cæca. 12, Rectum or
large intestine. 13, Cloaca. 14, Anus. 15, Liver. 16, Gall-bladder.
17, Pancreas. 18, Gizzard. 19, Trachea. 20, Lungs. 21, Spleen.
]

_Structure._—The free part of the tongue consists of two long tubes which are formed by the rolling in of the ventral sides of its horny coverings. The _dorsal plate_, which constitutes one-half of the horny sheath, does not form a part of the tubes, but ends in the region of the point of the entoglossum.

The top surface is covered by a thick stratum corneum, giving it a rather horny surface. Glands occur in the posterior part of the tongue.

While not so freely movable as in mammals, the tongues of birds are very flexible.

=The Pharynx= (Fig. 27). _Location._—The anterior part of the pharynx joins with the mouth and the posterior part with the upper portion of the esophagus and the superior larynx. The pharynx is bounded anteriorly by the base of the tongue and by the posterior edge of the hard palate. Posteriorly, it is marked by the entrance of the esophagus and by a ridge of filiform papillæ located on the supero-posterior part of the larynx, called the palatal papillaries. A few filiform papillæ stud the roof. The pharynx communicates anteriorly with the posterior nares and the mouth, and, posteriorly, with the esophagus and the larynx.

_Shape._—The pharynx is a musculo-membranous sac.

_Structure._—The pharynx is lined with a mucous membrane covered by squamous epithelium. The mucous membrane is thrown into irregular folds. The bird has two Eustachian tubes. Pneumatic apertures conduct the air from the Eustachian tubes to the pericranial diploë.

In the posterior pharyngeal roof is situated the infundibular crevice.

_Function._—The function of the pharynx is to give passage for the air from the posterior nares to the larynx, and to give passage for the food from the _mouth_ to the esophagus.

=Glands Adjacent to the Mouth and to the Pharynx.=—The mucous membrane adjacent to the glottis and in the roof of the mouth contains alveolar glands. The _angular gland_ of the mouth, located beneath the zygomatic arch, by some anatomists is considered the rudimentary parotid gland. The _sublingual glands_, or glandulæ sublinguales, are well developed (Fig. 17, No. _B_, 4). They form conical masses, with the apex directed anteriorly, and occupy a portion of the intermaxillary space. Several ducts from these glands open into the mouth cavity. In the palatine region there are also located glands called the _palatine glands_, which open by many stomata upon the surface.

=The Esophagus= (Fig. 18, No. 6). _Location and Shape._—The esophagus is a musculo-membranous tube, capable of great distension, which extends from the pharynx to the proventriculus (Fig. 35, No. 1, and 3).

The esophagus communicates anteriorly with the pharynx. It extends down the neck, lying supero-laterally with regard to the trachea and toward the right side. It enters the thorax above the trachea, and, passing through between the bronchi, terminates into the proventriculus. At the entrance of the thorax and just to the right of the median line, it expands into the crop which divides it into two portions, designated as the first and the second. The first portion of the esophagus is the longer, the length depending upon the size and kind of fowl.

_Structure._—The wall is composed of four coats, the mucous membrane, the submucosa, the muscular coats, and the fibrous sheath or tunic. The mucous membrane is pale and is covered with stratified squamous epithelium.

The mucous membrane is loosely attached to the muscular coat by the submucosa. Except during deglutition it lies in longitudinal folds which obliterate the lumen. Opening from the mucosa are lenticular glands, which may be seen on inflating an esophagus and looking through its transparent walls.

The muscular coat of the esophagus is divided into two layers, an outer longitudinal and an inner circular layer.

The outer fibrous sheath connects the esophagus loosely to the surrounding structures.

_Function._—The function of the esophagus is to give passage way for the food from the pharynx to the crop and from the crop to the proventriculus.

=The Crop= (Fig. 35, No. 2; Figs. 30 and 31). _Location and Shape._—The crop, or ingluvies, saccular in shape, is located at the entrance of the thorax and just to the right of the median line. The first portion of the esophagus empties into the crop superiorly and inferiorly the crop opens into the second portion of the esophagus. Like the esophagus the crop is capable of great distension.

_Structure._—The wall of the crop is composed of four coats, the mucous membrane, submucosa, muscular and the outer fibrous.

The crop is lined with mucous membrane containing mucous glands which secrete a mucus to keep the surface moist. The surface of the mucous membrane is covered by stratified squamous epithelium.

The submucosa connects the mucous membrane to the muscular coat.

The wall of the crop is provided with strong muscles. The fibrous coat, or tunic, connects it with the surrounding structures.

_Function._—The crop is a storehouse for the food during the hours of feeding, the food when needed by the stomach being gradually discharged from the crop by the contraction of its muscular walls. The subcutaneous cervical muscles which cover this reservoir aid in this discharge.

In the _act of deglutition_, the food, after being subjected to the fluid supplied in the mouth by the adjacent glands, is poised upon the tongue and swallowed partly by a sudden jerk of the head, and partly by means of the pressure of the tongue against the hard palate, the food then passes down the esophagus and lodges first in the crop, till needed by the stomach, when it is passed through the second portion of the esophagus to the first portion of the stomach, the proventriculus. The time during which food remains in the crop depends upon the nature of the food. Animal food will, in part, be retained about eight hours and vegetable foods may not all be passed on for from sixteen to eighteen hours.

=The Stomach= (Fig. 31, No. 7; Fig. 32, _B_).—The stomach, or ventriculus, of fowls is made up of two portions, namely, the pars glandularis, or proventriculus, and the pars muscularis, or gizzard.

=The Proventriculus.= _Location._—The proventriculus lies in the superior part of the groove formed by the two lobes of the liver, is inferior to the aorta, and is directed slightly to the left, communicating anteriorly with the second portion of the esophagus and posteriorly emptying into the pars muscularis, the gizzard.

_Shape._—The proventriculus is round transversely and elongated, in fact, nearly fusiform. In the hen of average size it measures about 1.62 inches long and 0.8 inch in diameter.

_Structure._—The wall of the proventriculus has four coats, the mucous, submucous, muscular, and serous.

The inner mucous coat which is raised in folds, is lined with columnar epithelial cells. The mucous membrane contains lymphoid tissue. The mucous coat throughout contains simple tubular glands which secrete a highly acid fluid which finds its way to the surface through small cylindrical ducts lying at right angles to the inner surface of the mucous membrane (Fig. 32, No. _B_, 1).

FIG. 32.—Gizzard and stomach of the fowl.

_A._ 1, Alveolar glands. 2, Mucous membrane of the inner surface of
the proventriculus showing the tubular glands. 3, Connective tissue
between the alveolar glands. 4, An artery. 5, Muscularis mucosa.

_B._ Photograph of the proventriculus and gizzard. 1, Proventriculus
showing stomata of glands. 2, End of duodenum. 3, Gizzard showing
hornified epithelium formed into grooves. 4, The heavy muscular
walls.
]

The submucosa, connects the mucous and muscular coats and the muscularis layer throws the mucous membrane into folds.

Outside the muscularis mucosa there is another layer (Fig. 32, _A_), of simple tubular glands, grouped in lobules, and lined by cuboidal cells and separated from each other by clefts. These tubular glands converge toward the center and open into the same cavity.

The middle muscular coat can be divided into three layers: two thin, longitudinal layers, and a thick, circular layer interposed between the other two.

_Function._—The function of the proventriculus appears to be to soak the food with a secretion. The secretion from the proventriculus is similar to that produced by the fundus glands of the stomach of mammals. It contains acid and a ferment-pepsin.

=The Gizzard= (Fig. 31, No. 18). _Location._—The gizzard, or muscular stomach, occupies a portion of the central part of the abdominal cavity (Fig. 33, No. 4). It lies slightly to the left and just behind the liver, the proventriculus, and the spleen, and rests upon a mass of intestines. The gizzard communicates at its anterior portion with the proventriculus and with the duodenum. These openings are close together. The gizzards of a large number of hens of average size averaged in weight as follows: full, 0.215 pound; empty, 0.126 pound. The gizzard stands perpendicularly and somewhat obliquely in the abdominal cavity.

_Shape._—In shape the gizzard is roundish, flattened laterally.

_Structure._—The walls of the gizzard are very thick and are made up of three coats: mucous, muscular, and serous.

The cavity of the gizzard is covered by a thick skin-like structure possessing a heavy stratified squamous epithelial layer which is thrown somewhat into ridges (Fig. 32, _B_). This membrane becomes thinnest near the edges.

The mucous membrane, being cornified and readily detachable, is by some anatomists considered as a special membrane (Fig. 37, _B_).

At the pyloric opening there is a valve formed by a fold of the mucous membrane, which prevents grit and large particles of food from passing out of the gizzard.

FIG. 33.—View of viscera of the left side of a hen. 1, The base of the
heart. 2, Proventriculus. 3, Left lobe of the liver. 4, Gizzard. 5,
End of the duodenal loop. 6, Pancreas. 7, Free portion of the small
intestine. 8, Lungs. 9, Diaphragm.
]

FIG. 34.—View of the viscera of the right side of a hen. 1, Base of
the heart. 2, Lungs. 3, Right lobe of the liver. 4, Duodenal loop.
5, Pancreas. 6, Cæcum. 7, Large intestine or rectum. 8, Free portion
of the floating small intestine. 9, Gall-bladder. 10, Right kidney.
11, The ribs. Note the lungs pushing up between them.
]

On each side it has a powerful fleshy muscle, the _muscularis lateralis_. These musculares laterales are hemispherical, consist of very closely packed fibers extending transversely, and are attached to strong anterior and posterior ligamentous tendons. They are joined at the edge of the organ by a strong aponeurosis. The muscular fibers are red but do not possess cross striations; they are of the smooth type. The _muscularis intermedii_, thinner and less developed than the musculares laterales, occurs on each of the anterior and the posterior parts of the gizzard.

The serous coat covers over the greater part of the external surface of the gizzard and closely adheres to the muscular coat.

_Function._—The hard callous pads of the gizzard, operated by the powerful muscles above described, together with grit, act like mill stones and make reduction to fineness very complete.

At the posterior part there is a sacculated portion containing glands of the long tubular type which secrete a fluid ferment similar to that secreted by the glands of the pyloric portion of the stomach of mammals. These glands also exist in a small band near the entrance of the gizzard. Here the food is mixed with strongly acid secretion containing pepsin which makes gastric digestion perfect.

FIG. 35.—A median antero-posterior section through the body of a
1-pound pullet. 1, First portion of the esophagus. 2, Crop. 3,
Second portion of the intestine. 4, Proventriculus. 5, Gizzard. 6,
Spleen. 7, Liver. 8, Heart. 9, Point where duodenum was severed from
gizzard. 10, Point where duodenum was severed. 11, Duodenum. 12,
Pancreas. 13, Cæcum. 14, Floating small intestine. 15, Ovary. 16,
Oil sac.
]

=The Small Intestine= (Fig. 31, No. 8 and 9).—The small intestine, intestinum tenue, is the tube which connects the gizzard with the large intestine. It is divided into two parts, the duodenum and the free portion. Of the three parts as considered in the mammalian intestine, only the first, the _duodenum_, can be distinguished. There is no demarcation between the jejunum and the ileum. The jejunum and the ileum or that part which represents these sections, are in coils suspended from the free border of the mesentery the other border of which is, in turn, attached to the dorsal wall (Fig. 64). The length of the small intestine in a hen of average size is about 61.7 inches.

FIG. 36.

_A._ Section of the duodenum of the fowl. 1, Villus. 2, Gland. 3, Mass
of lymphoid tissue. 4, Muscularis mucosa. 5, Longitudinal layer. 6,
Circular muscular layer. 7, Serous layer.

_B._ A section from A at _a_. 1, The striated free border of the
cells. 2, Goblet cell. 3, Columnar cell. 4, Nucleus of cell.
]

The wall of the small intestine is provided with four coats, as follows: a mucous, submucous, muscular coat made up of two layers—the outer, longitudinal and the inner circular layer, and an external serous.

FIG. 37.—Histological studies of various anatomical parts.

_A._ A transverse section of the first portion of the esophagus of a
fowl. 1, The outer longitudinal muscular layer. 2, The circular
muscular layer. 3, The submucosa. 4, The muscularis mucosa. 5,
Stroma. 6, Epithelial layer. 7, The lenticular glands. 8, The lumen.

_B._ A transverse section of the proventriculus. 1, The outer
longitudinal muscular layer. 2, The middle muscular layer. 3, The
inner longitudinal muscular layer. 4, Stroma. 5, The muscularis
mucosa. 6, The submucosa. 7, Stroma. 8, Tubular glands. 9,
Tubulo-alveolar glands. 10, A tubulo-alveolar gland with the tubular
glands cut transversely, 11, The lumen of the proventriculus.

_C._ A section of the inner wall of the gizzard. 1, The hyaline mucous
membrane. 2, Branched tubular glands. 3, Submucosa. 4, Muscle. 5, A
connective tissue septum.

_D._ A transverse section of the small intestines. 1, The outer
longitudinal muscular layer. 2, The inner circular muscular layer.
3, The muscularis mucosa. 4, The stroma. 5, Brunner’s glands. 6, A
villus. 7, Mass of lymphoid tissue.

_E._ A transverse section through the cecum. 1, The outer longitudinal
muscular layer. 2, The inner circular muscular layer. 3, The
submucosa. 4, The muscularis mucosa. 5, The stroma. 6, Tubular
glands. 7, The lumen.

_F._ The cerebellum showing the arbo-vitæ. 1, White, fiber portion. 2,
The granular layer. 3, The layer of Purkinje cells. 4, The molecular
layer.
]

The mucous membrane which lines the intestine is thick, soft, and highly vascular. It has a velvety appearance, due to numerous long, thin projecting _villi_. The villi (Fig. 36, _A_) are concerned in the absorption of the digested food, absorbing principally the emulsified fats. Each villus is covered with a single layer of high columnar epithelial cells. Some of these, the so-called goblet cells, provide mucin which lubricates the mucous surface. These cells are found in all mucous surfaces and prevent the surface from becoming dry. There are a few goblet cells near the summits of the villi. Openings of simple intestinal tubular glands the duodenal glands, or the glands formerly known as _Brunner’s glands_, are located between the villi. These glands secrete the succus entericus, or intestinal juice. These openings, or stomata, are lined with granular cells. The reaction of the contents of the small intestine is strongly acid, but gradually less so in proportion to the distance down the intestinal tract until the cæca are reached, where the reaction is found to be faintly acid, neutral, or slightly alkaline.

_Function._—The function of the small intestine is that of digestion and absorption.

=The Duodenum.= _Location and Shape._—The duodenum, a small tube, originates from the gizzard about ½ inch to the right of the entrance of the proventriculus. Extending from left to right, it passes under and behind the gizzard along the inner side of the right abdominal wall backward to the posterior portion of the wall, and a trifle more than half way toward the left side, where the loop rests. This loop, the duodenal loop, is about 5 inches in length (Fig. 31, No. 8). The two branches of the loop the first and the second portions or the descending and ascending limbs, are loosely held by connective tissue, and have the pancreas lodged between them.

=The Free Portion of the Small Intestine.= _Location._—That section of the small intestine following the duodenum is called the free portion of the small intestine and occupies the space between the abdominal air-sac and the median line of the abdominal cavity. It is disposed in coils and is suspended from the dorsal wall of the abdomen by a thin membrane, the mesentery.

The bile ducts enter the small intestine about 14 inches from its point of origin. The pancreas also pours its contents into the small intestine.

=The Large Intestine= (Fig. 31, No. 12). _Location._—The large intestine extends in a straight line along the inferior border of the vertebral column communicating anteriorly with the small intestine, and the cæca and posteriorly with the cloaca.

_Shape._—The diameter of the large intestine is approximately twice that of the small intestine. In fowls of average size its mean length is 4.61 inches. The large intestine has sometimes been spoken of as the rectum, or straight gut.

_Structure._—Like the small intestine the large intestine has four coats: an inner mucous, a submucous, a middle muscular and an outer serous. The folds of mucous membrane of the large intestine have tubular glands lined with columnar cells (Fig. 37, _A_, No. 1).

_Function._—The large intestine is similar in function to that of the small intestine, in that digestion and absorption may take place within it.

=The Cæca= (Fig. 31, No. 11). _Location._—The fowl has two cæca extending forward from their point of origin at the juncture of the small and large intestine.

_Shape._—The cæca average 7.61 inches in length. They are large in caliber toward the blind extremity and are constricted near their origin.

_Structure._—The parietal coats are continued from the small intestine.

Ebarth has described an elevated body in the cæcum, which is located about 4 millimeters from the opening and is composed entirely of lymphoid tissue.

FIG. 37_A_.—Photomicrograph of a transverse section of large intestine
and oviduct just anterior to the cloaca, showing the tubular glands
of the large intestines, mucosa of oviduct with intervening
structures. 1, The tubular glands of large intestine, or rectum. 2,
Muscular wall of intestine. 3, Wall of the oviduct. 4, Mucosa of the
oviduct.
]

The cæca are usually partly filled with a soft pultaceous material of a pasty consistency.

=The Cloaca= (Fig. 31, No. 13). _Location._—The rectum opens by a circular, valvular orifice into the dilated portion just in front of the anus, which dilatation is called the cloaca.

_Shape._—The cloaca is saccular in shape.

_Structure._—The cloaca is divided into two portions, the coprodeumal and the urodeumal. That portion of the cloaca into which the intestine empties is called the _coprodeum_; and the ureter and oviduct empty into the _urodeum_. The seminiferous tubules, carrying the semen from the testes in the male empty in teatlike projections on the cloacal mucous membrane into the urodeumal portion. The cloacal walls are similar in structure to the large intestines.

On the dorsal wall of the cloaca between it and the spine, is a small sac, called the _bursa of Fabricius_, which has a duct communicating with the cloaca. The mucous membrane of this sac is thrown into folds and is studded with glands. The bursa of Fabricius is larger in the young than in the adult bird. It apparently atrophies as the bird becomes older. When the bird is four months old this bursa is best developed, and at this age it may be as large as 2 or 3 centimeters in diameter.

_Function._—The function of the cloaca is to give passage way to the feces, the urine, and the egg and to act as an organ of copulation.

=Course of the Food.=—The food first enters the mouth, after being picked up by aid of the beak. From here it passes through the pharynx and first portion of the esophagus to the crop, without mastication, as the bird is not provided with teeth. The food is passed from the crop by aid of its muscular walls as needed; thence through the second portion of the esophagus to the proventriculus, an expansion in the digestive tube just before it terminates in the gizzard. The glands of the proventriculus produce a secretion in which the food is soaked before passing into the gizzard. The gizzard is provided with strong muscular walls which, by aid of grit, thoroughly reduce the food to fineness. From the gizzard the food passes through the first portion of the small intestine, where it is subjected to the action of the bile from the liver, the pancreatic juice from the pancreas, and of the succus entericus from the glands of the intestinal wall. The food is then passed into the cæca. The indigestible portion of the food passes from the cæca through the large intestine, or rectum, to the cloaca and thence to the external world.

The digestive functions of the bird are very potent and rapid. This compensates for the waste caused by their extensive, frequent, and energetic motions, and is in accordance with the rapidity of their circulation and their high state of irritability.

THE ACCESSORY ORGANS OF DIGESTION

The accessory organs of digestion are the liver, pancreas, and some anatomists include also the spleen. The first two manufacture fluids containing ferments which aid in splitting or digesting the food.

=The Liver= (Figs. 31, 33 and 34). _Location._—The liver, hepar, lies ventrally and posteriorly to the heart. It is related anteriorly with the diaphragm, inferiorly with the sternum, posteriorly with the gizzard and intestine, and superiorly with the ovary, oviduct and proventriculus and laterally with the abdominal wall.

_Shape._—The liver is a voluminous deep livid brown gland, soft and friable in texture. It is divided into two principal lobes, a right and a left.

The right lobe is larger than the left. In the hen of average size the liver weighs 35 grams. The parietal surface is convex and smooth. The surface which lies against the viscera is irregularly concave. The visceral surface furnishes exit for the bile duct and passage for the nerves and blood-vessels. This part is called the porta.

The left lobe may be cleft from below so deeply as to form two lobes on that side.

_Structure._—Each lobe is covered by a double serous membrane, one closely adherent, the other surrounding the structure loosely. These tunics, which are reflections of the peritoneum, are continued from the base of the liver, over both the anterior, and the posterior surface. The loose layer is formed by the air cells surrounding the lobes. The thin border of the liver is usually free.

The two lobes of the liver are connected by a narrow isthmus of liver tissue. Occasionally there is a bird in which there occurs a _lobus Spigelii_ located at the posterior of the liver between the two principal lobes.

The apex of the heart sacculates the diaphragm backward, so that part of this apex lies between the right and the left lobes (Fig. 43, No. 6 and 7). A ligament, the _falciform_, extends from the apex of the pericardial membrane, and attaching it rather firmly to the central connective tissue, or interlobar ligament. This ligament also has attachments to the inner surface of the sternum. The _broad ligament_ of the liver is formed posteriorly by a fold of the peritoneum.

The _interlobar_, or _principal, ligament of the liver_ is formed by a large and strong duplicature of the peritoneum, which makes a longitudinal division in the abdominal cavity similar to the lateral division made by the thoracic mediastinum in mammals. It is reflected upon the pericardium from the linea alba and the middle line of the sternum, and passes deeply into the interspace of the lobes of the liver. It is attached to these lobes throughout their whole length and connects them below to one side of the gizzard. The lateral and posterior part of the liver attach to the adjacent air cells, and the whole viscus is thus kept fixed in its position during rapid and violent movements of the bird.