Part 30

=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.