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

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

=Trachelo-mastoideus= (Fig. 19, No. 16). (Synonym.—Longissimus capitis et atlantis.)

_Location._—Laterally on the anterior portion of the neck.

_Origin._—Semitendinous from the diapophyses of the second, the third, the fourth, and the fifth cervical vertebræ.

_Insertion._—By subcompressed tendon to the base of the cranium, at the outer tubercle of the basal ridge of the basi-temporal.

_Shape._—Flattened from side to side; broad at the posterior portion, becomes angular at the anterior portion.

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

=Interspinales= (Fig. 17, _A_, No. 2). _Location._—Superior to the vertebra.

_Origin and Insertion._—A series of muscles connecting the superior neural spines of the cervical vertebræ.

_Shape._—Thin, flat.

_Relations._—Anteriorly the posterior border of the vertebræ in front and posteriorly the anterior border of the succeeding vertebræ, inferiorly by the vertebræ.

_Action._—To approximate the spinous portion of the vertebræ.

=Interarticulares= (Fig. 17, No. _A_, 4). _Location._—Supero-laterally to the vertebræ. Between the postzygapophysis.

_Origin and Insertion._—From the posterior margin of the ring of the atlas to the postzygapophysis of the axis. Then in the succeeding vertebræ from the postzygapophysis of the vertebra to the same of the succeeding vertebra.

_Shape._—Muscular bundle.

_Relations._—Inferiorly with the vertebræ. Supero-laterally with the obliquo-transversales.

_Action._—Aids in approximating the vertebræ in a supero-lateral direction.

=Obliquo-transversales= (Fig. 17, _A_, No. 1). _Location._—Supero-lateral to the vertebræ.

_Origin and Insertion._—Passes obliquely from the transverse process of one vertebra to the postzygapophysis of the vertebra beyond.

_Shape._—A thin fasciculus.

_Relations._—Inferiorly with the interarticulares and laterally with the intertransversales.

_Action._—Aids in flexing the vertebræ supero-laterally.

=Intertransversales= (Fig. 19, No. 12). _Location._—Laterally to the vertebræ.

_Origin and Insertion._—Extend between the transverse processes beginning at the third cervical vertebra.

_Shape._—Short, thick.

_Relations._—Laterally the vertebræ. Superiorly the obliquo-transversales.

_Action._—Aids in flexing the vertebræ laterally.

=Scalenus Medius= (Fig. 19, No. 18). (Synonym.—Scalenus.)

_Location._—Supero-laterally to the entrance of the thorax.

_Origin._—From the diapophysis and pleurapophysis of the eleventh cervical vertebra.

_Insertion._—To the entire border of the first rib. A few fibers pass over to the anterior free margin of the middle third of the second rib.

_Shape._—Rather pyramidal in shape with base uppermost.

_Relations._—Posteriorly with the levatores costarum. Internally with the longus colli.

_Action._—When the first rib is fixed singly, turns the neck to one side; acting with its fellow, extends the neck. When the neck is fixed, by drawing the first rib forward, it acts as an inspiratory muscle.

THE MUSCLES OF THE AIR PASSAGES

The Superior Larynx

Constrictor glottidis
Thyreo-arytenoideus

The Inferior Larynx

Tracheo-lateralis
Broncho-trachealis posticus
Broncho-trachealis anticus
Broncho-trachealis brevis
Bronchialis posticus
Bronchialis anticus
Sterno-trachealis

=Constrictor Glottidis.= _Location._—Supero-anterior portion of the superior larynx.

_Origin._—From the superior and longitudinal line of the thyroid plate.

_Insertion._—All along the inner margin of the arytenoid bone, and to the apex of the mid-cricoidal segment.

_Shape._—Thin, flat sheet extending outward and upward, and then inward.

_Relation._—Interiorly with the larynx.

_Action._—The two muscles of this kind acting together, close the glottis by drawing the apices of the arytenoids to the median line.

=Thyreo-arytenoideus.= _Location._—Supero-lateral portion of the superior larynx.

_Origin._—From the entire outer margin of the thyroid plate and the outer margin of the cricoid bone.

_Insertion._—All along the outer margin of the arytenoid bone and the outer border of the central cricoid piece.

_Shape._—A thin, flat sheet.

_Relations._—Infero-laterally with the superior larynx.

_Action._—The two muscles of this kind acting together, open the glottis by pulling the arytenoid bone outward.

=Tracheo-lateralis= (Fig. 20, No. 2). _Location._—Along the lateral side of the trachea.

_Origin._—By the union of the bronchio-trachealis posticus and bronchio-trachealis anticus, on the lateral side of the trachea, about 1½ centimeters from the bifurcation of the trachea.

_Insertion._—In delicate fan-like structure to the side of the trachea, near the superior larynx.

_Shape._—Thin, ribbon-shaped, closely attached to the trachea.

_Relations._—Internally with the trachea, and externally with the skin and other integument.

_Action._—Acts as a brace to the sides of the trachea, and contracting, approximates the tracheal rings and thus shortens the trachea.

=Broncho-trachealis Posticus= (Fig. 21, No. 3). _Location._—Postero-superior portion of the trachea. The fibers pass downward and backward.

_Origin._—From the inferior end of the tracheo-lateralis.

_Insertion._—To the end of the third half of the bronchial ring of the same side.

_Shape._—A small fasciculus.

_Relations._—Internally with the trachea, and externally with the skin and other integument.

FIG. 20.—The anterior pectoral region. 1, Sterno-trachealis. 2,
Tracheo-lateralis. 3, Broncho-trachealis brevis. 4, Costal process
of sternum. 5, Right and left carotid converging and occupying same
sheath at 6. 7, The heart showing branches of coronary artery. 8,
Cervical air-sac. 9, Left brachio-cephalic artery. 10, Right
brachio-cephalic artery. 11, Trachea. 12, Inferior larynx. 13.
Subclavian artery. 14, Carotid trunk. 15, Internal thoracic artery.
16 Thyroid gland. 17, Anterior vena cava. 18, Auricular appendage.
]

FIG. 21.—The inferior tracheal region. 1, Bronchialis anticus. 2,
Bronchialis posticus. 3, Broncho-trachealis posticus. 4,
Broncho-trachealis anticus.
]

_Action._—A tensor of the true or inferior larynx.

=Broncho-trachealis Anticus= (Fig. 21, No. 4). _Location._—Anterior portion of the inferior extremity of the trachea.

_Origin._—The anterior branch of the bifurcated tracheo-lateralis.

_Insertion._—To the anterior extremity of the third half ring of the bronchus of the same side.

_Shape._—A small fasciculus.

_Relations._—Internally with the trachea, and externally with the skin and other integument.

_Action._—A tensor of the inferior larynx.

=Broncho-trachealis Brevis= (Fig. 20, No. 3). _Location._—Posterior part of the inferior extremity of the trachea.

_Origin._—From just beneath the broncho-trachealis anticus muscle.

_Insertion._—Extends obliquely across the inferior larynx and is inserted to the posterior end of the second bronchial ring.

_Shape._—Rather short, strong, straight, subcylindrical.

_Relations._—Internally with the trachea, and laterally with the broncho-trachealis posticus.

_Action._—A tensor of the inferior larynx.

=Bronchialis Posticus= (Fig. 21, No. 2). _Location._—Supero-lateral side of the anterior end of the bronchi.

_Origin._—From the lateral inferior margin of the last tracheal ring.

_Insertion._—Passing obliquely across the larynx it inserts to the posterior extremity of the second half ring of the bronchus.

_Shape._—Small, thick, spindle-shaped.

_Relations._—Internally with the trachea, inferiorly with the bronchialis anticus, and superiorly with the broncho-trachealis brevis.

_Action._—A tensor of the larynx.

=Bronchialis Anticus= (Fig. 21, No. 1). _Location._—Inferior to the former muscle.

_Origin._—From the last ring of the trachea.

_Insertion._—The fibers pass obliquely forward and become inserted to the rim of the arytenoid cartilage of the inferior larynx, and the anterior extremities of the first and second half rings of the bronchus.

_Shape._—Thick, spindle-shaped; about twice the size of the bronchialis posticus.

_Relations._—It is crossed at its origin by the broncho-trachealis anticus and is related internally with the bronchus and end of the trachea.

_Action._—A tensor of the larynx.

=Sterno-trachealis= (Fig. 20, No. 1). _Location._—The inferior region of the trachea above the above-named muscles.

_Origin._—From the side of the trachea beneath the posterior border of the broncho-trachealis anticus.

_Insertion._—Passes downward and backward across the cavity of the chest and is inserted to the inner part of the costal process of the sternum.

_Shape._—A delicate cord of fibers.

_Relations._—Internally with the broncho-trachealis muscles.

_Action._—A relaxor of the larynx, and hence, of the tympanic membrane.

THE STERNAL GROUP

=Triangularis Sterni.= _Location._—In the floor of the thoracic cavity.

_Origin._—From the entire superior margin of the summits of the costal processes.

_Insertion._—The fibers extend upward and backward, dividing into four digitations which cover the inner surface of the three principal sternal ribs, and are inserted to the first four as high as their articulations with the vertebral ribs.

_Shape._—Flat and somewhat triangular.

_Relations._—Interiorly with the floor of the thoracic cavity.

_Action._—A powerful muscle of expiration. In contracting, lessens the cubic content of the thorax.

=The Diaphragm= (Fig. 47, No. 10; Fig. 33, No. 9). _Description._—The diaphragm in the domestic fowl is rudimentary. It consists of a thin semi-transparent membrane, situated between and separating the thoracic and the abdominal cavities. It readily conforms to the various organs pressing upon it from each side. On each side are three rudimentary muscles which extend from the vertebral heads of the second, the third, and the fourth sternal ribs. The fibers of these muscles spread out in fan-like upon the diaphragm, and are seen just above the digitations of the triangularis sterni.

THE ABDOMINAL MUSCLES

Obliquus abdominis externus
Obliquus abdominis internus
Rectus abdominis
Transversalis abdominis

=Obliquus Abdominis Externus= (Fig. 22, No. 1). _Location._—The outermost muscle of the lateral abdominal wall.

_Attachments._—By a delicate aponeurotic membrane, from the sides of all the true dorsal ribs, from the posterior border of the last vertebral rib and the adjoining margins of the pelvis, and from the entire posterior surface of the inferior border of the post-pubic element of the pelvis; by aponeurosis, blending with the fascia toward the root of the tail and lower part of the abdomen; and by aponeurosis to the sides of the sternum, to the under part of the pectoralis major muscle, and to the zyphoid prolongation. Also by aponeurosis it meets its fellow from the opposite side, at the linea alba.

FIG. 22.—The abdominal muscles of a hen. Right side. 1, Obliquus
abdominis externus. 2, Obliquus abdominis internus. 3, Peritoneum
covering intestines. 4, Peritoneum covering the gizzard. 5, The
lungs (note how small they are from a relative standpoint). 6, The
great sciatic or ischiadic nerve. 7, Lumbar nerves. 8, Kidney. 9,
Brachial plexus. 10, Pericardium of the base of the heart. 11,
Anterior vena cava. 12, Oil gland. 13, Showing a sacculation of the
abdominal muscles. There is no tunica abdominalis in the fowl.
]

=Obliquus Abdominis Internus= (Fig. 22, No. 2). _Location._—Just internal with regard to the external oblique.

_Attachments._—By aponeurosis, from the posterior third of the post-pubic element of the pelvis; by muscular fibers, from the balance of the bone; and by a few fibers, from the iliac border posterior to the acetabulum. Anteriorly, these fibers are inserted to the entire posterior margin of the last vertebral rib, and into the pleurapophysial head of the last costal rib.

=Rectus Abdominis= (Fig. 13, No. 10 and Fig. 23, No. 1). _Location._—The inferior median abdominal wall.

_Attachments._—By aponeurosis, from the distal extremity of the post-pubic element of the pelvis and from the semitendinous ligament which stretches from one post-pubic tip to the other. Attaches anteriorly to the zyphoid margin of the sternum, and passes, by a broad aponeurotic membrane, over the outer surface of the thoracic wall beneath the external oblique.

=Transversalis Abdominis= (Fig. 25, No. _H_, 1). _Location._—Infero-lateral portion of the abdominal wall.

_Attachments._—By a thin, tendinous attachment from the entire post-pubic and iliac margins of the pelvis and from the interpubic ligament. Its fibers cross the abdomen between the peritoneum, the rectum, and the internal oblique. It is inserted over the entire pleural part of the last two vertebral ribs, the intercostal muscles between them, and the same surface of the hemapophyses connected below. Inserts into the linea alba.

_Action._—The abdominal muscles give support to the abdominal organs, aid in flexing the spine, draw the last rib backward, thus aiding in respiration, and compress the abdominal organs to aid in defecation and expiration.

THE DORSO-LUMBAR REGION

Sacro-lumbalis
Longissimus dorsi

=Sacro-lumbalis.= _Location._—The lateral lumbo-sacral region.

_Origin._—Tendinous from the anterior margin of the ilium, from the angles of the last two vertebral ribs, and by tendinous slips, from the outer ends of the transverse processes of the last three dorsal vertebræ.

_Insertion._—By a few fleshy fibers into the angle of the first dorsal rib and to the corresponding points upon the free cervical ribs, and by a strong semitendinous insertion into the outer extremity of the diapophysis of the twelfth cervical vertebra.

_Shape._—A close fitting, tendo-muscular sheet extending between the anterior margin of the ilium and the root of the neck.

_Relations._—Intimately blended with the longissimus dorsi externally.

_Action._—Assists the longissimus dorsi.

=Longissimus Dorsi= (Fig. 24, No. 4). _Location._—The superior dorso-lumbar region.

_Origin._—From the inner portion of the anterior margin of the ilium, and from the various surfaces afforded by its walls and the walls of the ilio-neural canal; by a series of short and distinct tendons alternately from the anterior and posterior extremities of the summits of the neural spines of all the dorsal vertebræ. From the diapophyses of the dorsal vertebræ, from the crests of the neural spines of the last three dorsal vertebræ, from the bodies of the dorsal vertebræ, and from the fascia between them and the sacro-lumbalis; and also by a tendinous sheet continuous with the origin of the longus colli posticus.

_Insertion._—By four fasciculi into the free posterior margins of the oblique processes of the eleventh, the twelfth, the thirteenth, and the fourteenth cervical vertebræ.

_Shape._—A large flat sheet.

_Relations._—Laterally, with the superior spinous processes of the vertebræ, and with the superior surface of the ribs.

_Action._—Singly, flexes the back laterally; with its fellow, aids in elevating the body upward.

THE COCCYGEAL MUSCLES

Levator coccygis
Levator caudæ
Transversus peronei
Depressor caudæ
Depressor coccygis
Lateralis caudæ
Lateralis coccygis
Infracoccygis

=Levator Coccygis= (Fig. 23, No. 2). _Location._—The superior part of the caudal apparatus.

_Origin._—From a limited area of the ilium just beyond and to the side of the anterior free caudal vertebræ.

_Insertion._—Into the tuberosity of the anterior margin of the pygostyle.

_Shape._—Short, fleshy.

_Relations._—Superior portion of the coccygeal vertebræ.

_Action._—Elevates the tail.

=Levator Caudæ= (Fig. 23, No. 4). _Location._—Supero-lateral side of the tail.

_Origin._—From the posterior surface of the post-acetabular area of the pelvis, and from the superior surface of all the coccygeal vertebræ except the pygostyle.

_Insertion._—To the four inner quill butts of the main tail feathers.

_Shape._—Long, spindle-shaped.

_Relations._—Internally, with the levator coccygis and externally, with the lateralis caudæ.

_Action._—Powerfully elevates the four inner main tail feathers.

=Transversus Peronei= (Fig. 23, No. 3). _Location._—The posterior abdominal region.

FIG. 23.—Outer layer of muscles of the tail and thigh, 1, Rectus
abdominis. 2, Levator coccygis. 3, Transversalis peronie. 4, Levator
caudæ. 5, Lateralis caudæ. 6, Depressor caudæ. 7, Sartorius. 8 and
9, Gluteus primus. 10, Semitendinosus. 11, Gastrocnemius. 12,
Peroneus longus. 13, Flexor perforatus indicis secundus pedis. 14,
Flexor perforatus medius secundus pedis. 15, Lateral ligament of the
hock.
]

_Origin._—From the entire posterior margin of the ischium, and from the posterior margin of the post-pubis extending beyond it.

_Insertion._—Becoming aponeurotic, it passes toward the coccyx and is attached to the entire posterior margin of the ilium. Passes to the median line, meeting its fellow in front of the anus.

_Shape._—Thin, sheet-like.

_Relations._—Infero-anteriorly with the anus. Posteriorly with the edges of the ilium and of the ischium. Internally with the depressor caudæ.

_Action._—Gives support to the viscera in the post-anal region, and aids in attaching the anus to the structures above.

=Depressor Caudæ= (Fig. 23, No. 6). _Location._—The infero-lateral side of the tail.

_Origin._—From the lower half of the posterior border of the ischium, and from the entire posterior border of the post-pubis beyond.

_Insertion._—To the quill butts of the three or four outer main tail feathers.

_Shape._—Strong, conical.

_Relations._—Externally, with the depressor coccygis.

_Action._—Singly, pulls the tail downward and outward; with its fellow, pulls the tail downward.

=Depressor Coccygis.= _Location._—The outermost of the infero-lateral muscles of the tail.

_Origin._—From the lower half of the posterior margin of the ischium and the anterior three-fourths of the posterior margin of the post-pubic element of the pelvis beyond it.

_Insertion._—To the thickened rim of the inferior and expanded portion of the pygostyle.

_Shape._—Flat, triangular.

_Relations._—Internally with the depressor caudæ.

_Action._—Singly, pulls the tail downward and to one side; with its fellow, pulls the tail downward.

=Lateralis Caudæ= (Fig. 23, No. 5). _Location._—The lateral side of the tail.

_Origin._—From the tip of the transverse process of the first free caudal vertebræ.

_Insertion._—To the outer three quill butts of the main tail feathers.

_Shape._—Four fasciculi forming a fleshy belly.

_Relations._—Inferiorly, with the levator caudæ and superiorly with the depressor caudæ.

_Action._—Singly, pulls the tail downward and outward; with its fellow, pulls the tail downward. The outermost fasciculus contracting, spreads the tail feathers.

=Lateralis Coccygis= (Fig. 25, No. _E_, 2). _Location._—The infero-lateral side of the caudal vertebræ.

_Origin._—From the surface of the posterior end of the ilium and by tendons from the under side of the ends of the first three or four caudal vertebræ.

_Insertion._—To the side of the posterior margin of the expanded portion of the pygostyle.

_Shape._—Subcompressed mass.

_Relations._—With the transverse processes of the caudal vertebra, inferiorly.

_Action._—Controls the lateral movements of the tail and its feathers, and the oblique downward movement.

=Infracoccygis= (Fig. 25, No. _E_, 1). _Location._—The extreme inferior portion of the caudal vertebræ.

_Origin._—From the inferior surface of the diapophysis of the last vertebra which anchyloses with the pelvic sacrum, and from all the free caudal vertebræ.

_Insertion._—Into the lower side of the pygostyle.

_Shape._—Flat, somewhat triangular.

_Relations._—Superiorly, with the vertebræ, laterally, with the lateralis coccygis, and mesially, with its fellow of the opposite side.

_Action._—Depresses the tail.

THE COSTAL REGION

Latissimus dorsi
Trapezius
Rhomboideus
Serratus magnus anticus
Serratus parvus anticus
Teres et infraspinatus
Intercostales
Levatores costarum
Appendico-costales

=Latissimus Dorsi= (Fig. 24, No. 7). _Location._—Supero-lateral portion of the dorsal region.

_Origin._—From two portions, the anterior slip from the outer edge of the superior margins of the neural spines of the second and the third dorsal vertebræ, and the second portion from a similar point on all the succeeding dorsal vertebræ. The second portion is fascia-like in its attachments.

_Insertion._—The fibers converge toward the humerus and enter between the deltoid the scapular head of the triceps and the remaining heads of this muscle and is inserted to the anconal part of the humerus, just within in the radial crest.

_Shape._—Thin, triangular.

_Relations._—Superiorly, with the skin. The most superficial of the dorsal muscles.

_Action._—To elevate the humerus and thus flex the shoulder-joint. An expiratory muscle when the wing is fixed.

=Trapezius= (Fig. 19, No. 20). _Location._—In the shoulder region, just below the longissimus dorsi.

_Origin._—From the neural spines of the second, the third, the fourth, and the fifth cervical vertebræ just below the latissimus dorsi.

_Insertion._—To the mesian upper border of the scapula.

_Shape._—A flat oblong layer of fibers.

_Relations._—The posterior part of the trapezius overlies the anterior part of the rhomboideus. The posterior two-thirds is covered by the latissimus dorsi. The anterior third is superficial.

_Action._—Draws the scapula forward.

=Rhomboideus= (Fig. 19, No. 19). _Location._—Supero-posterior scapular region.

_Origin._—From the neural spines of the first four dorsal vertebræ beneath the latissimus dorsi and trapezius muscles.

_Insertion._—The fibers passing outward and backward attach to the posterior third of the mesial or upper border of the scapula.

_Shape._—Thin, flat, delicate.

_Relations._—Superiorly, by the latissimus dorsi and the trapezius.

_Action._—To draw the free end of the scapula upward and forward.

=Serratus Magnus Anticus= (Fig. 13, No. 16). _Location._—The supero-lateral side of the thorax.

_Origin._—By three strong digitations: first, from the outer part of the second true rib just above the base of the epineural appendage; the other two, from similar locations on the two succeeding ribs, just above the origin of the dermo-ulnaris.

_Insertions._—The first by tendinous attachment to the interpleurapophysial membrane. The rest of the fibers pass upward and slightly forward, and are inserted to the inferior surface of the apex of the scapula.

_Shape._—Three flat, strong digitations.

_Relations._—Internally, with the ribs.

_Action._—If the scapula is fixed, it is a muscle of inspiration.

=Serratus Parvus Anticus.= _Location._—The outer and upper surface of the anterior part of the thorax.

_Origin._—By three digitations from the outer surface of the first three ribs above the origin of the serratus magnus anticus and the thoraco-scapularis.

_Insertion._—The thin sheet of fibers passes upward and backward, and is inserted to the inferior margin of the scapula.

_Shape._—Thin, flat.

_Relations._—Internally, with the ribs.

_Action._—If the scapula is fixed, it is a muscle of respiration.

=Teres et Infraspinatus= (Fig. 13, No. 11). _Location._—Scapular region.

_Origin._—From the superior surface and outer margin of the posterior two-thirds of the scapula.

_Insertion._—The fibers pass forward and outward, and insert to the humerus at the middle of the ulnar margin of the pneumatic fossa, between the forks of the triceps.

_Shape._ —Flat, triangular-shaped.

_Relations._—Anteriorly, with the supraspinatus. Internally, with the ribs.

_Action._—Aids in keeping the humerus in its socket. Assists in closing the wing by drawing the humerus to the side of the body.

=Intercostales= (Fig. 24, No. 5). _Location._—Between the ribs of the upper thoracic region.

_Origin and Insertion._—From the anterior border of one rib, the fibers, passing obliquely upward and forward, and the lower portion downward and forward, are inserted to the posterior border of the rib just in front.

_Shape._—They are best developed in the anterior portion of the thoracic region and extend down as far as the sternal ribs.

_Relations._—Internally the pleura, and anteriorly and posteriorly the ribs.

_Action._—The first rib being rendered fixed by the scalenus medius, the muscles draw the ribs forward, thus aiding inspiration.

=Levatores Costarum= (Fig. 24, No. 2). _Location._—Supero-lateral portion of the thorax.

_Origin and Insertion._—A series of muscles, the first of which extends from the extremity of the transverse process of the twelfth vertebra, the fibers passing downward and backward to the anterior free margin of the upper third of the long posterior rib, and to the external surface close to its margin. The others arise and insert in a similar manner from the ends of the diapophyses of all the dorsal vertebræ and attach to each succeeding rib. Those in front are best developed.

_Shape._—Thin and triangular.

_Relations._—External to the intercostales.

_Action._—Aids in respiration.

=Appendico-costales= (Fig. 24, No. 1). _Location._—The lateral side of the thorax.

_Origin and Insertion._—From the posterior edge of an uncinate process or epineural appendage, the fibers extending downward and backward to the outer surface of the succeeding rib.

_Shape._—A series of thin triangular-shaped muscles.

_Relations._—Internally, with the intercostales.

_Action._—Aids in respiration.

THE ANTERIOR PECTORAL GROUP

Tensor patagii longus
Tensor patagii brevis

=Tensor Patagii Longus= (Fig. 15_C_, No. 1; Fig. 14, No. 2). _Location._—Anterior shoulder region, in the triangular patagium of the wing.

_Origin._—By a flat tendon common to it and the tensor patagii brevis from the supero-mesial line of the head of the clavicle.

_Insertion._—By a long slender tendon extending in the duplicature of the patagium, with which the fibers blend. Passing to the side of the extensor metacarpi radialis longus, it extends over the end of the radius and is inserted to the os carpi radiale, and to the fascia which binds down the other tendons on the anterior part of the wrist-joint.

_Shape._—Cone-shaped belly terminating in a long tendon.

_Relations._—Externally, with the skin; by its tendon, with the border of the extensor metacarpi radialis longior.

_Action._—Tenses the soft part in the fold of the wing, and aids in flexing the forearm.

=Tensor Patagii Brevis= (Fig. 14, No. 3). _Location._—In the triangular patagium of the wing.

_Origin._—From the head of the clavicle in common with the preceding.

_Insertion._—The tendon bifurcates, one branch blending with the fascia of the extensor metacarpi radialis longior, the other inserting just below the tubercle on the external condyle of the humerus.

_Shape._—Fleshy; somewhat broader and longer than the preceding.

_Relations._—Interiorly, with the preceding.

_Action._—Assists the tensor patagii longus in flexing the forearm.

THE PECTORAL MUSCLES

Pectoralis major
Pectoralis secundus
Pectoralis tertius

=Pectoralis Major= (Fig. 13, No. 5). _Location._—On the lateral side of the sternum.

_Origin._—From the posterior portion of the lateral wing of the sternal body, from the outer marginal third of the keel of the sternum, and from the entire outer side of the limb of the furcula or clavicle.

_Insertion._—The fibers converging form toward the proximal third of the humerus a broad tendon which by its insertion covers the entire palmar part of the pectoral crest. A few of the tendinous fibers pass over the shoulder-joint and blend with the long head of the biceps. Near this point it receives the insertion of the dermo-humeralis.

_Relations._—Interiorly, with the skin; superiorly, in the sternal region, with the pectoralis secundus and the pectoralis tertius.

_Shape._—Fleshy; largest of the pectorales.

_Action._—Powerfully depresses the humerus. The chief muscle of flight.

=Pectoralis Secundus= (Fig. 13, No. 9; Fig. 15, No. _A_, 6). _Location._—The entire lateral side of the sternum.

_Origin._—From the anterior sternal extremity of the lower third of the coracoid, from the keel and sternal wing, and by a tendon from a membraneous expansion between the coracoid and the clavicular bones and from the lower third of the coracoid.

_Insertion._—The fibers converge into a tendon, which passes upward around the coracoid to its posterior through a canal formed by the scapula, the coracoid, and the clavicle, the foramen triosseum (Fig. 15, No. _A_, 7). This tendon then passes outward and downward, and becoming flat, inserts to the humerus just anterior to the radial crest and nearer to the humeral head than does the pectoralis major.

_Relations._—Internally, with the breast-bone; externally, with the pectoralis major; and superiorly, with the pectoralis tertius.

_Shape._—Long, fusiform, fleshy.

_Action._—Raises the wing.

=Pectoralis Tertius= (Fig. 13, No. 6; Fig. 15, No. _A_, 5). _Location._—On the antero-lateral side of the sternum.

_Origin._—From the anterior half of the exterior of the body of the sternum, from the fascia of the subclavius on the outer border of the costal process, and from the outer, lower third of the coracoid process.

_Insertion._—The fibers pass upward to the outer side of the coracoid, and becoming tendinous as they reach the humerus, by a strong flattened tendon insert to the ulnar crest of the humerus on the proximal margin at about a middle point of the pneumatic fossa.

_Relations._—Externally, with the pectoralis major; interiorly, with the pectoralis secundus; internally, with the fascia of the subclavius and the sternum.

_Shape._—Fleshy, fusiform.

_Action._—Assists the pectoralis secundus in elevating the humerus.

MUSCLES OF THE SCAPULAR REGION

Coraco-humeralis
Scapulo-humeralis
Supraspinatus
Subclavius
Coraco-brachialis
Teres minor
Levator scapulæ
Thoraco-scapularis
Subscapularis

=Coraco-humeralis.= _Location._—The scapulo-humeral region.

_Origin._—From the outer side of the head of the coracoid, supero-laterally to the long head of the biceps.

_Insertion._—To the palmar part of the head of the humerus just inside of the insertion of the pectoralis major.

_Shape._—A delicate subcylindrical muscle.

_Relations._—Superior to the head of the humerus.

_Action._—Aids in extending the humerus.

=Scapulo-humeralis= (Fig. 14, No. 10). _Location._—The scapulo-humeral region.

_Origin._—From the inner side of the neck of the scapula just within the head of the deltoid.

_Insertion._—Passing over the top of the shoulder-joint it is inserted to the palmar part of the humeral head between the insertion of the pectoralis major and the pectoralis secundus.

_Shape._—Narrow, flat ribbon.

_Relations._—Along the upper margin of the larger portion of the deltoid.

_Action._—Aids in extending the humerus.

=Supraspinatus= (Fig. 19, No. 22). _Location._—Scapular region.

_Origin._—From the superior surface and outer third of the scapula.

_Insertion._—To the lower border of the pneumatic fossa of the humerus.

_Shape._—Thin, flat, triangular.

_Relations._—Externally, with the trapezius and posteriorly, with the teres et infraspinatus.

_Action._—If the scapula is the fixed point it will pull the humerus upward and backward.

=Subclavius.= _Location._—Anterior sternal region.

_Origin._—From the entire outer surface of the sternal process of the sternum and the adjacent outer surfaces of three or four of the hemapophyses.

_Insertion._—To the inferior margin of the coracoid bone, the longer fibers passing over to the fossa in the lower third of the posterior part of the coracoid.

_Shape._—Rather small, fleshy.

_Relations._—Overlapped by the pectoralis tertius.

_Action._—Pulls the coracoid outward. Also aids in keeping the coracoid in place.

=Coraco-brachialis= (Fig. 13, No. 15). _Location._—Along the coracoid shaft.

_Origin._—By a delicate tendon from a small circular point on the postero-mesial part of the shaft of the coracoid immediately above the attachment of the subclavius and the fossa at that point.

_Insertion._—To the top of the ulnar tuberosity of the humerus. This subcircular space is common to the teres minor and to this muscle.

_Shape._—Long, fusiform.

_Relations._—With the shaft of the coracoid between the teres minor and subscapularis.

_Action._—To depress the wing.

=Teres Minor= (Fig. 13, No. 14). _Location._—The coraco-scapular region.

_Origin._—From under the side of the anterior tip of the scapula.

_Insertion._—Passing outward behind the coracoid head and beneath the neck of the scapula, it is attached by a small tendon to the top of the ulnar tuberosity of the humerus in common with the coraco-brachialis, with which tendon it fuses.

_Shape._—Small, chunky.

_Relations._—Anteriorly, with the tip of the scapula and behind the coracoid head. Posteriorly, with the coraco-brachialis.

_Action._—Aids in the downward stroke of the wing.

=Levator Scapulæ.= _Location._—Scapular region.

_Origin._—By two strong digitations, one from each of the lateral processes of the first cervical vertebra.

_Insertion._—To the middle third of the inferior part of the blade of the scapula.

_Shape._—Small and flat.

_Relations._—Inferior to the scapula.

_Action._—Pulls the scapula forward, and with it the entire shoulder girdle, which articulates like a hinge-joint at the costo-sternal juncture.

=Thoraco-scapularis.= _Location._—Lateral side of the chest.

_Origin._—From the outer part of the lower half of the first free rib, the outer side of the next succeeding rib and its epineural appendage, and from a similar surface on the next rib.

_Insertion._—By a broad, flat tendon which passes between the two divisions of the subscapularis and inserts at a point at the juncture of the anterior and middle third of the outer margin of the scapula.

_Shape._—Broad, flat.

_Relations._—Internally, with the ribs and the scapula.

_Action._—When the scapula is fixed it is a muscle of inspiration. When the ribs are fixed, it draws the scapula downward.

=Subscapularis.= _Location._—Scapulo-humeral region.

_Origin._—From the anterior and outer half of the scapula.

_Insertion._—By a strong and subcylindrical tendon to the top of the ulnar tuberosity of the humerus close to the combined tendons of the coraco-brachialis and teres minor.

_Shape._—A large and powerful muscle.

_Relations._—The flat tendon of the thoraco-scapularis divides the posterior portion of the belly into two portions.

_Action._—A powerful rotary muscle of the head of the humerus; aids in keeping the humeral head in the glenoid cavity.

THE MUSCLES OF THE BRACHIAL REGION

Biceps
Triceps
Deltoid
Brachialis anticus

=Biceps= (Fig. 13, No. 8). (Synonym.—Biceps brachii.)

_Location._—The anterior brachial region.

_Origin._—By a broad tendon it covers the top of the shoulder-joint, dividing into two heads, giving rise to the long and the short heads. The long is inserted into the outer part of the head of the coracoid just beyond the glenoid cavity; the short head to the distal angle of the ulnar tuberosity of the humerus.

_Insertion._—To the ulna just in front of the articular cavity for the trochlear surface of the distal extremity of the humerus.

_Shape._—Large, subfusiform.

_Relations._—On one side by the triceps and the other the deltoid and anteriorly partially covered by the patagii muscles.

_Action._—A powerful flexor of the forearm.

=Deltoid= (Fig. 13, No. 12; Fig. 15, No. 8). _Location._—Occupying the lateral side of the humerus; the brachial region.

_Origin._—Divided into two portions, the long narrow head extends from the clavicular process of the scapula and from the adjacent surface of the same bone. These fibers then extend around the back of the shoulder-joint, and are joined by the fibers that arise from the entire outer surface of the large os humero-scapulare. These latter fibers are inserted upon an extensive area upon the anconal part of the bone beyond the humeral articular head, and to almost the entire shaft below it.

_Insertion._—By a subcylindrical tendon to the proximal side of the tubercle of the external condyle, and above the insertion of the extensor metacarpi radialis longus.

_Shape._—Large, fleshy, with tendinous attachment.

_Relations._—On one side by the biceps and the other by the triceps also the patagii.

_Action._—To extend the arm.

=Triceps= (Fig. 15, No. 7). (Synonym.—Triceps brachii.)

_Location._—The posterior humeral region.

_Origin._—By three portions: by the internal and external heads, and by the long scapular head. The internal and the external heads are blended except at their proximal extremities. Each head arises from the anconal surface of the shaft of the humerus. The internal head being located toward the deltoid attachment and the external head into the pneumatic fossa. The long head extends from a circumscribed area just posterior to the glenoid cavity of the scapula. The fibers pass around the shoulder-joint, beneath the deltoid.

_Insertion._—The broad tendon passes over the elbow-joint and is inserted to the entire under surface of the olecranon of the ulna.

_Shape._—Long, large, fleshy.

_Relations._—The supraspinatus passes between the internal and the external heads. It is bounded by the biceps and the deltoid.

_Action._—An extensor of the antibrachial region directly antagonizing the biceps.

=Brachialis Anticus= (Fig. 15, No. 9; Fig. 14, No. 5). _Location._—In the flexure of the humerus and the ulna.

_Origin._—It arises fleshy from a circumscribed area on the inner side of the anconal part of the distal extremity of the humerus.

_Insertion._—The fibers passing directly over the elbow-joint become inserted to the lateral surface of the proximal end of the ulna close to the margin of the sigmoid cavity.

_Shape._—Small, fleshy.

_Relations._—With the joint.

_Action._—Assists in flexing the forearm upon the arm. Protects the structures in the anterior part of the elbow-joint.

THE MUSCLES OF THE FOREARM AND THE HAND

Extensor metacarpi radialis longior
Supinator brevis
Extensor digitorum communis
Pronator brevis
Flexor metacarpi radialis
Extensor ossis metacarpi pollicis
Pronator longus
Extensor indicis longus
Flexor digitorum sublimis
Flexor digitorum profundus
Flexor carpi ulnaris
Flexor carpi ulnaris brevior

=Extensor Metacarpi Radialis Longior= (Fig. 13, No. 17). _Location._—Superior to the radius.

_Origin._—By two strong tendinous heads; the outer from the tubercle of the external condyle of the humerus, just above the origin of the tendon of the tensor patagii brevis; the inner and stronger portion from the tubercle found above the oblique trochlear facet of the distal end of the radius.

_Insertion._—Becoming a flat, broad, and strong tendon at about the middle of the forearm, finally becomes inserted to the apex of the anchylosed first metacarpal of the carpo-metacarpus.

_Shape._—A thick, fusiform belly, tendinous at both extremities.

_Relations._—By the side of the pronator brevis.

_Action._—Raises the hand, and draws it forward toward the radial margin of the forearm and retains it on the same side.

=Extensor Digitorum Communis= (Fig. 15, No. 2). _Location._—The upper metacarpal region.

_Origin._—Immediately below the tubercle of the external condyle of the humerus.

_Insertion._—By a small tendon to the outer side of the base of the pollex, and at a mid-point upon the anterior rim of the proximal phalanx of the middle finger.

_Shape._—Small spindle-shaped, becoming tendinous at about the middle of the forearm.

_Relations._—Occupies the middle of the group of muscles on the outer side of the forearm.

_Action._—An extensor of the digit.

=Supinator Brevis= (Fig. 14, No. 7). _Location._—The superior part of the radius.

_Origin._—From the external condyle of the humerus below the origin of the tendon of the extensor digitorum communis.

_Insertion._—To the outer side of the shaft of the radius, for nearly one-third of its length.

_Shape._—Thin, slender.

_Relations._—Inferiorly, with the bone.

_Action._—A supinator of the radial region, and antagonistic to the pronators.

=Flexor Metacarpi Radialis= (Fig. 15, No. 10). _Location._—The lowest of the group of three muscles on the outer part of the forearm.

_Origin._—By two tendinous heads, the longer from the external condyle of the humerus, and the other just beyond the base of the olecranon.

_Insertion._—Becomes tendinous at about the middle of the shaft of the ulna and inserts to a prominent process on the proximal third of the posterior part of the shaft of the mid-metacarpal.

_Shape._—Fusiform.

_Relations._—Inferiorly, the anconeus and superiorly, the extensor digitorum communis.

_Action._—A powerful flexor of the hand.

=Pronator Brevis= (Fig. 13, No. 18). _Location._—Supero-lateral side of the forearm.

_Origin._—From just above the internal condyle of the humerus.

_Insertion._—The tendon passing obliquely across the interosseous space and is inserted to the ulnar side of the shaft of the radius, just beyond the juncture of the proximal and the middle thirds.

_Shape._—Fusiform.

_Relations._—Superior to the pronator longus.

_Action._—Pronates the forearm, and flexes the forearm upon the arm.

=Pronator Longus= (Fig. 14, No. 6). _Location._—Lateral side of the radio-ulnar region.

_Origin._—From the middle of the internal condyle of the humerus.

_Insertion._—To the shaft of the radius just beneath the pronator brevis.

_Shape._—Massive, ellipsoidal.

_Relations._—Between the pronator brevis and flexor digitorum profundus.

_Action._—A pronator.

=Extensor Ossis Metacarpi Pollicis= (Fig. 13, No. 23). _Location._—Slightly interposed between the ulna and radius.

_Origin._—Immediately in front of the greater sigmoid cavity of the ulna.

_Insertion._—To the palmar side of the base of the first metacarpal, in common with the extensor metacarpi radialis longior.

_Shape._—Delicate, straight.

_Relations._—Superiorly, the extensor indicis longus, and inferiorly, the anconeus and the flexor digitorum profundus.

_Action._—Extends the hand upon the forearm.

=Anconeus= (Fig. 15, No. 4). _Location._—Between the ulna and the radius.

_Origin._—By a short, strong, subcylindrical tendon from the lower posterior of the external condyle of the humerus.

_Insertion._—To the latero-radial side of the ulna somewhat beyond its middle.

_Shape._—Fusiform.

_Relations._—Superiorly, the extensor indicis longus, and inferiorly, the ulna.

_Action._—A flexor of the forearm.

=Extensor Indicis Longus= (Fig. 13, No. 22; Fig. 15, No. 13). _Location._—Infero-lateral to the radius.

_Origin._—From about one-half the surface of the proximal portion of the radius.

_Insertion._—Possesses a long tendon which passing over a groove at the distal end of the ulna and receiving muscular fibers at the base of the metacarpus, extends down the anterior part of the hand and is inclosed in a sheath in front of the superior part of the first phalanx of the index-finger. This tendon is inserted into the anterior upper rim of the distal phalanx.

_Shape._—Small, thin.

_Relations._—Supero-laterally with the radius.

_Action._—Extensor of the digit.

=Flexor Digitorum Sublimis.= _Location._—The forearm.

_Origin._—From the internal condyle of the humerus.

_Insertion._—Passing over the wrist, it is inserted to the middle phalanx of the hand.

_Shape._—A musculo-tendinous band, rather delicate and rudimentary.

_Relations._—Closely adhering to the integument that stretches from the internal condyle of the humerus to the wrist.

_Action._—Assists these muscles. A flexor.

=Flexor Digitorum Profundus= (Fig. 13, No. 21). _Location._—Lateral side of the ulna.

_Origin._—By two heads from the proximal extremity of the ulna, between which the brachialis anticus passes.

_Insertion._—The two bellies uniting are attached to the under side of the shaft of the ulna. It becomes tendinous about the middle of the shaft, and inserts to the ulnar side of the base of the distal joint of the index-finger.

_Shape._—A fleshy belly with long tendon.

_Relations._—Inferiorly, with the flexor carpi ulnaris, superiorly, with the pronator brevis.

_Action._—A flexor of the digit.

=Flexor Carpi Ulnaris= (Fig. 13, No. 19). _Location._—Inferior part of the forearm.

_Origin._—By two strong tendons; one from the side and posterior of the internal condyle of the humerus, passing through the humero-ulnar pulley at the side of the base of the olecranon process; the other, to the posterior of the internal condyle of the humerus. It does not pass through a pulley.

_Insertion._—A subcylindrical tendon extends back of the ulnare ossicle of the carpus giving off a tendinous slip to the flexor digitorum profundus, and becomes inserted to the anterior rim of the proximal phalanx of the index digit. It has an attachment at the carpus.

_Shape._—A strong fleshy belly terminating in a long tendon.

_Relations._—The outermost inferior muscle of the forearm.

_Action._—A powerful flexor of the hand upon the forearm.

=Flexor Carpi Ulnaris Brevior= (Fig. 13, No. 20). _Location._—Inferior part of the antibrachial region.

_Origin._—From a broad area on the middle third of the upper side of the shaft of the ulna.

_Insertion._—Near the top of the outer edge of the anchylosed os magnum of the carpo-metacarpus.

_Shape._—Thin, somewhat flat.

_Relations._—To the inside of the flexor digitorum profundus.

_Action._—Flexes the hand upon the forearm and rotates the hand toward the body.

OTHER MUSCLES OF THE DIGITS

Extensor proprius pollicis
Flexor minimi digiti
Abductor minimi digiti
Interosseous palmaris
Flexor brevis pollicis
Flexor minimi digiti brevis
Interosseous dorsalis
Flexor metacarpi brevis

=Extensor Proprius Pollicis= (Fig. 13, No. 29a). _Location._—Anterior to the radio-carpal joint.

_Origin._—From the ulnar side of the tendon of the extensor metacarpi radialis longior.

_Insertion._—To the antero-ulnar side of the pollex.

_Shape._—Small, spindle-shaped; tendinous at both attachments.

_Relations._—Inferiorly, with the proximal and anterior part of the metacarpus.

_Action._—An extensor of the pollex.

=Flexor Brevis Pollicis= (Fig. 13, No. 28a). _Location._—Anterior to the pollex.

_Origin._—From the shaft of the mid-metacarpal bone, just below the pollex.

_Insertion._—Distal apex of the pollex.

_Shape._—Short, small, fleshy.

_Relations._—Superiorly, with the inferior part of the pollex.

_Action._—Flexes the pollex.

=Flexor Minimi Digiti.= _Location._—Inferior side of the metacarpus.

_Origin._—From the posterior part of the median metacarpal close to the os carpi ulnare. A few fibers extend to the ulna.

_Insertion._—Into the base of the median phalanx.

_Shape._—Small, slender, short.

_Relations._—Superiorly, with the metacarpal bone.

_Action._—A flexor of the digit.

=Flexor Minimi Digiti Brevis= (Fig. 13, No. 30). _Location._—Inferior to the third, or small finger.

_Origin._—From the lower and posterior end of the median metacarpal and from the adjacent tendon of the preceding.

_Insertion._—Inserted to the apex of the small finger.

_Shape._—Small and rather rudimentary.

_Relations._—Inferior to the small finger.

_Action._—Acts as a posterior ligament of this joint.

=Abductor Minimi Digiti.= _Location._—Supero-lateral side of the small finger.

_Origin._—From the proximal extremity of the anterior aspect of the third finger.

_Insertion._—To the posterior border of the proximal phalanx of the second, or index-finger at a point just above the tip of the third finger.

_Shape._—A few muscular fibers with some tendinous material.

_Relations._—At the base of the median segment of the index-finger and to the side of the third.

_Action._—Antagonizes the powerful flexors on the back of the joint.

=Interosseus Dorsalis= (Fig. 13, No. 31). _Location._—By the side of the metacarpus.

_Origin._—From the margin of the shaft of the median metacarpal.

_Insertion._—To the anterior part of the base of the distal phalanx of the index digit.

_Shape._—Short, delicate, with long tendon.

_Relations._—Internally, the metacarpal bone.

_Action._—Extends the last bone of the middle finger.

=Interosseus Palmaris= (Fig. 13, No. 32). _Location._—On the opposite side of the bone from the interosseous dorsalis.

_Origin._—From the shaft of the median metacarpal under the preceding.

_Insertion._—To the apex of the last joint of the second, or middle finger.

_Shape._—Small, delicate, with long slender tendon.

_Relations._—Beneath the preceding and along the metacarpal bone.

_Action._—Flexes the terminal phalanx.

=Flexor Metacarpi Brevis.= _Location._—To the lateral side of the metacarpal bone.

_Origin._—From the outer side of the distal extremity of the ulna.

_Insertion._—To the base, in front, and on the ulnar side of the proximal phalanx of the index digit.

_Shape._—Delicate, with long slender tendon.

_Relations._—On the lateral side of the ulna and the metacarpal bone.

_Action._—Flexes the metacarpus.

MUSCLES OF THE POSTERIOR LIMB

Sartorius
Gluteus medius
Extensor femoris
Biceps flexor cruris
Semitendinosus accessorius
Femoro-caudal
Obturator internus
Abductor longus
Gluteus primus
Gluteus minimus
Vastus internus
Semitendinosus
Semimembranosus
Obturator externus
Gemellus
Adductor magnus

=Sartorius= (Fig. 23, No. 7). _Location._—Extreme anterior portion of the thigh.

_Origin._—From the outer two-thirds of the superior surface of the raised emarginations of the anterior border of the ilium, and by fascia from the neural spines of the fourth dorsal vertebra.

_Insertion._—Obliquely by a semitendinous fascia to the inner edge of the ligamentum patella, and to the inner and adjacent border of the anterior half of the summit of the tibia.

_Shape._—Large, fleshy.

_Relations._—Posteriorly, with the gluteus primus and the vasti.

_Action._—Extends the leg, flexes and adducts the thigh.

=Gluteus Primus= (Fig. 23, No. 8 and 9). _Location._—The outer flat massive muscle of the thigh.

_Origin._—By a thin fascia from nearly the entire length of the supero-internal margin of the pre-acetabular portion of the ilium, above the antitrochanter, and from the entire length of the post-acetabular ridge.

_Insertion._—Near the patella it joins the tendon of the extensor femoris, and by aponeurosis spreads over the knee and is inserted to the crest of the upper border of the tibia, the patella being incorporated in its aponeurotic ligament.

_Shape._—Triangular in shape, it is aponeurotic anteriorly and more fleshy posteriorly.

_Relations._—Anteriorly, covers over the posterior portion of the sartorius and the body of the gluteus medius; posteriorly, bordered by the semitendinosus and the biceps.

_Action._—Abducts the thigh.

=Gluteus Medius= (Fig. 24, No. 11). _Location._—Supero-anterior part of the ilium under the gluteus primus.

_Origin._—From the entire supero-internal margin of the pre-acetabular surface of the ilium and the concave surface on the adjacent bone.

_Insertion._—By a strong tendon which passes over a bursa on the anterior rim of the trochanter and is inserted obliquely to this trochanter.

_Shape._—A fleshy muscle filling the concavity of the pre-acetabular division of the ilium.

_Relations._—Superiorly, with the gluteus primus; inferiorly, with the gluteus minimus.

_Action._—Abducts and pulls the femur forward.

=Gluteus Minimus= (Fig. 24, No. 12). (Synonym.—Gluteus profundus.)

_Location._—Beneath the medius and the smaller of the two.

_Origin._—To the anterior margin of the outer border of the ilium, and from the supero-external surface of the last rib.

_Insertion._—The fibers extending downward and backward and outward become tendinous and are inserted below the trochanter of the outer part of the upper third of the femur.

_Shape._—Small, fleshy.

_Relations._—Inferiorly, with the bone and superiorly, with the gluteus medius.

_Action._—Abducts and pulls the thigh forward.

=Extensor Femoris= (Fig. 24, No. 15). _Location._—Anterior femoral region. It is divided into two parts: the vastus externus and the crureus.

_Origin._—The vastus extemus (Fig. 24, No. 14) arises tendinous from the base of the trochanter of the outer part of the femur and from this point down the bone approximately to the condyle. The crureus (Fig. 24, No. 13) originates by a tendon from the anterior upper prominent rim of the trochanter, from this point extending down the antero-external part of the shaft of the femur.

_Insertion._—Merges with the gluteus primus, and, by a fascia-like arrangement, spreads over the front of the knee-joint inserts to the patella and is also inserted into the crest of the tibia.

_Shape._—Large, fleshy.

_Relations._—Posteriorly, with the femur and anteriorly, with the sartorius.

_Action._—Extends strongly the leg upon the thigh.

=Vastus Internus= (Fig. 16, No. 3). _Location._—Internal and lateral side of the femur.

_Origin._—From the postero-internal part of the shaft of the femur just below the head, and in a straight line extending down the femur.

_Insertion._—By a broad tendon along the thickened inner border of the summit of the tibia.

_Shape._—Thick, long.

_Relations._—Anteriorly, with the bone; surrounded by the other crural muscles.

_Action._—Extends the leg upon the knee; a powerful assistant of the extensor femoris.

=Biceps Flexor Cruris= (Fig. 17, No. D, 1). _Location._—Posterior tibial region.

_Origin._—By a tendinous fascia from the post-acetabular ridge, extending between the antitrochanter and the anterior point of the insertion of the semitendinosus.

_Insertion._—To the tuberosity on the external part of the shaft of the fibula a short distance below the head.

_Shape._—Large, rather cone-shaped with base directed upward.

_Relations._—Anteriorly, with the vastus externus; posteriorly, with the semitendinosus. The inferior tendinous portion passes through a tendinous sling or pulley called the biceps band.

_Action._—Flexes the leg upon the thigh.

=Semitendinosus= (Fig. 23, No. 10). _Location._—Posterior femoral region.

_Origin._—By a tough, strong fascia from the surface of the caudal muscles and from the posterior third of the post-acetabular ridge.

_Insertion._—The fibers pass downward and forward, and insert to the tendinous raphe along the posterior margin of the semitendinosus accessorius; lower down it merges with the median fascia of the inner head of the gastrocnemius.

_Shape._—Fleshy, broad, flat and long.

_Relations._—Internally, with the semimembranosus and anteriorly, with the biceps flexor cruris.

_Action._—Flexes the leg.

=Semitendinosus Accessorius.= _Location._—Posterior femoral region.

_Origin._—From an oblique line just above the condyle, on the posterior of the shaft of the femur.

_Insertion._—Its fibers, passing upward and backward, attach themselves to the tendinous raphe common to this muscle and the semitendinosus, and are finally inserted to the inner side of the shaft of the tibia.

_Shape._—Flat, oblong.

_Relations._—Posteriorly to the shaft of the femur, and externally to the long adductors of the thigh.

_Action._—Aids the preceding in flexing the leg.

=Semimembranosus= (Fig. 24, No. 17). _Location._—Postero-internal to the semitendinosus.

_Origin._—From the outer surface of the ischium, beginning at the lower margin of its notch on the posterior pelvic border, extends on a curved line on the adjacent surface beyond.

_Insertion._—The fibers, passing downward and forward, insert by a broad, thin tendon to the shaft of the tibia a short distance below the head and on a line parallel to the long axis of the tibia.

_Shape._—Long, narrow, ribbon-shaped.

_Relations._—Lies adjacent to the semitendinosus and in the same plane.

_Action._—Directly flexes the leg.

=Femoro-caudal= (Fig. 24, No. 8). _Location._—Infero-lateral to the caudal and post-femoral region.

_Origin._—By a delicate tendon from the base of the pygostyle.

_Insertion._—By a thin, flat tendon upon the outer part of the shaft of the femur below the trochanter and at about the juncture of the upper and middle third of the bone.

FIG. 24.—Second layer of muscles of the thigh of a cock. Outside view.
1, Appendico-costales. 2, Levatores costarum. 3, Sacro-lumbalis. 4,
Longissimus dorsi. 5, Intercostales. 6, Longissimus dorsi. 7,
Latissimus dorsi. 8, Femoro-caudal. 9, Edge of obturator externus.
11, Gluteus medius. 12, Gluteus minimus. 13, Crureus. 14, Vastus
externus. 15, Extensor femoris. 16, Biceps flexor cruris. 17,
Semimembranosus. 18, Adductor magnus. 19, Adductor longus. 20,
External abdominal oblique. 21, Depressor coccygis. 22, Tibialis
anticus. 23, Tibialis posticus. 24, Flexor perforans digitorum
profundus. 25, Flexor perforatus medius secundus pedis. 26, Flexor
longus hallucis.
]

_Shape._—Long, narrow, spindle-shaped, flattened from side to side.

_Relations._—Interiorly to the obturator externus, and along the upper border of the long adductors of the thigh and the semimembranosus.

_Action._—Pulls the tail down and to one side.

=Obturator Externus= (Fig. 24, No. 9). _Location._—External posterolateral side of the pelvis.

_Origin._—From the posterior half of the periphery of the ischiatic foramen and the concavity found on the external surface of the lateral part of the pelvis.

_Insertion._—The fibers pass across to the femur and are inserted by a broad, flat tendon to the shaft of the femur just below the trochanter.

_Shape._—Thick, fleshy.

_Relations._—Lies just above the femoro-caudal muscle, the sciatic nerve and femoral artery pass over and external to its tendon.

_Action._—Pulls the head of the femur backward.

=Obturator Internus= (Fig. 16, No. _E_, 1). _Location._—Occupies the space between the ischium and the pubis.

_Origin._—From the ventral surface of the ischium, including the posterior border, from the inner line of the corresponding post-pubis, and from the membrane covering the space between these two bones.

_Insertion._—Becoming dense, subcylindrical, and strong, it passes through the obturator foramen and is inserted to the outer part of the trochanter of the femur, in common with the gemellus and opposite to the insertion of the gluteus medius.

_Shape._—Subtriangular and flat with a central tendon; bipenniform.

_Relations._—Outside the pelvis the tendon lies upon the gemellus and is external to it. Fills the obturator foramen and the space between the ischium and the pubis.

_Action._—Acts as a posterior stay to the head of the femur.

=Gemellus= (Fig. 25, No. 5). _Location._—Posterior to the head of the femur.

_Origin._—From the fossa between the acetabulum and the obturator foramen, and on the outer side of the pelvis.

_Insertion._—Its fibers are attached by fascia to the tendon of the obturator internus, and pass directly to the trochanter of the femur where they insert in common with that of the obturator internus.

_Shape._—Strong, thick, chunky.

_Relations._—Postero-external to the head of the femur.

_Action._—Like the two preceding, when the head of the femur is fixed, it pulls the pelvis forward and steadies it on the head of the femur.

=Adductor Longus= (Fig. 24, No. 19). _Location._—In the posterior femoral region.

_Origin._—From a line on the lateral part of the pelvis.

_Insertion._—The fibers, passing downward and forward, are inserted on a longitudinal line along the posterior part of the shaft of the femur.

_Shape._—Broad, flat, fleshy.

_Relations._—Posteriorly to the femur, and anteriorly to the adductor magnus.

_Action._—Adducts the thigh.

=Adductor Magnus= (Fig. 24, No. 18). _Location._—Posterior femoral region.

_Origin._—From the fine constituting the lower boundary of the ischiatic fossa on the outer lateral part of the pelvis.

_Insertion._—The fibers pass downward and are inserted to the superior curve of the internal femoral condyle. The internal head of the gastrocnemius blends with this muscle just above its attachment.

_Shape._—Long, narrow.

_Relations._—Posteriorly to the adductor magnus and anteriorly to the semimembranosus.

_Action._—Strongly adducts the thigh.

THE TIBIAL GROUP

Gastrocnemius
Peroneus longus
Extensor longus digitorum
Tibialis posticus
Flexor longus hallucis
Flexor perforatus annularis primus pedis
Flexor perforatus medius secundus pedis
Flexor perforans digitorum profundus
Soleus
Tibialis anticus
Extensor hallucis brevis
Flexor perforatus indicis secundus pedis
Flexor perforatus medius primus pedis
Flexor perforatus indicis primus pedis
Extensor brevis digitorum
Flexor hallucis brevis
Extensor annularis brevis

=Gastrocnemius= (Fig. 23, No. 11). _Location._—Posterior tibial region.

_Origin._—There are three heads: the internal, the external, and the tibial. The external head extends by a short, flattened, strong tendon from the postero-external part of the external condyle of the femur; the internal head extends from the outer surface of the inner condyle of the femur; and the tibial head extends from the entire inner rim of the tibial summit and from the free edge of the adjacent crest.

_Insertion._—At the lower fourth of the tibial shaft, terminates in a broad, flat tendon which passes over the shallow, longitudinal groove of the tibial cartilage, and, crossing the tibio-tarsal joint, is inserted to the posterior surface of the hypotarsus of the metatarsal bone, and finally, below this point, merges into the podothecal sheath confining the flexor tendons.

_Shape._—Large, fleshy, somewhat cone-shaped with the base upward.

_Relations._—The posterior fleshy muscle of the post-tibial region located anterior to the soleus.

_Action._—Extends the metatarsus on the tibia.

=Soleus= (Fig. 25, No. _G_, 1). _Location._—The posterior tibial region.

_Origin._—From the posterior part of the head of the tibia.

_Insertion._—By a long slender tendon to the proximal end and toward the inner angle of the tibial cartilage, some of the fibers passing to the tendon of the gastrocnemius.

_Shape._—Small, flattened.

_Relations._—Anteriorly, with the flexor perforans digitorum profundus and posteriorly, with the gastrocnemius.

_Action._—Similar to that of the gastrocnemius.

=Peroneus Longus= (Fig. 23, No. 12). _Location._—Antero-lateral tibial region.

_Origin._—From the raised crest in front of the head of the tibia, and from the fascia that covers the outer side of the knee-joint.