Part 29

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