Part 32

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.