Part 27

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.