Part 28

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.