36 INTRODUCTION. 



vertebrcT. The first, 3 a, is inserted into the coracoid bone, the 

 other, 3 ^, into the middle of the linea aspera, or dorsal ridge of 

 the humerus, which it draws toward the back. 



The other muscles which arise from the trunk, to be inserted 

 into the humerus, are situated in front. 



4. Pectoralis major ^ Fig. 2, arises from the whole length 

 of the crest of the sternum, from its posterior and lateral mar- 

 gins, and from the outer edge of the furcula, forming a trian- 

 gular mass of vast size, sometimes exceeding in bulk all the 

 other muscles of the body together. Its fibres run obliquely 

 forwards and outwards, pass over the shoulder joint, and are 

 inserted fleshy into the anterior or upper crest of the head of the 

 humerus, and by a flat tendon where they cross the insertion of 

 the next muscle. Its action has not been correctly described. 

 Its anterior part raises the humerus, and brings it forward ; its 

 middle part brings the wing downward ; and its posterior part 

 brings the humerus backward, close to the body. Its combined 

 action is powerfully to depress the wing, and bring its anterior 

 edge downward, by which the quills are obliquely raised. 



5. Under the great pectoral muscle is seen, in Fig. 4, the 

 •pectoralis medius. It arises, properly speaking, over the other, 

 from the whole length of the under surface of the sternum, and 

 the upper half of its crest, and from the fore edge of the cora- 

 coid bone and the membrane between it and the furcula. The 

 fibres converge into a central tendon, extending its whole length, 

 which passes forwards between the coracoid bone and furcula, 

 curves round the joint, and is inserted upon the upper tubercle 

 or crest of the humerus, close to the insertion of the pectoralis 

 major, and anterior to it. Although this muscle is similar in 

 its origin to the pectoralis major, its action, owing to the direc- 

 tion of its tendon, is the reverse of that muscle, as it elevates 

 the humerus and brings it forward. 



6. The pectoralis minor is a small muscle which arises from 

 the lower two-thirds of the outer edge of the coracoid bone and 

 the anterior margin of the sternum, under the articulation of 

 the ribs, forms a small round tendon, which passes outwards 

 and forwards, and is inserted into a prominent internal tubercle 

 of the humerus, which it pulls downwards and backwards. 



