_Insertion._—By a long slender tendon extending in the duplicature of the patagium, with which the fibers blend. Passing to the side of the extensor metacarpi radialis longus, it extends over the end of the radius and is inserted to the os carpi radiale, and to the fascia which binds down the other tendons on the anterior part of the wrist-joint. _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.