100 . ANATOMY OF THE DOMESTIC FOWL 



Shape. Fleshy; somewhat broader and longer than the preceding. 



Relations. Inferiorly, 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. Inferiorly, with the skin; superiorly, in the sternal 

 region, with the pectoralis secundus and the pectoralis tertius. 



Shape. Fleshy; largest of the pecto rales. 



Action. Powerfully depresses the humerus. The chief muscle 

 of flight. 



Pectoralis Secundus (Fig. 13, No. 9; Fig. 15, No. A, 6). Lo- 

 cation. 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 up- 

 ward around the coracoid to its posterior through a canal formed by 

 the scapula, the coracoid, and the clavicle, the foramen triosseum 

 (Fig. 15, No. -4,7). 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. 



