STERNAL MUSCLES. 321 



excusable but necessary ; and when the object is to 

 communicate information, that is not the very best 

 taste which sacrifices perspicuity to mere nicety, and 

 plainness of expression to what is (often very falsely) 

 considered elegance of style. 



The first set of muscles are those which have their 

 insertion in the sternum, the coracoid bone, and the 

 clavicle, and their tendons attached to the humerus ; 

 and these are the muscles which perform the grand ope- 

 ration of working the wing. They are four in number. 



The first, the great pectoral muscle, is situated 

 externally toward the anterior part of the sternum, 

 where it has the freest action. It is inserted on the 

 keel and body of the sternum, on the side of the 

 coracoid, and also on that of the clavicle ; and its 

 tendon, which is particularly strong and firmly united 

 by a large extent of surface, is attached to the 

 extended crest of the humerus on the lower side. 

 When this muscle contracts, it bends down the hume- 

 rus on the shoulder-joint ; but as it is inserted in all 

 the bones by which that joint is supported, the very 

 same action which bends down the humerus on the 

 joint, tends to push the joint upwards, which not only 

 renders the effect of the pulling of the tendon more 

 steady, but actually increases its force. This is the 

 grand muscle in flying, and it is impossible to imagine 

 an organ better situated or altogether better adapted 

 for its purpose than it is in birds of powerful flight. 



Immediately under this there is situated the middle 

 pectoral muscle, which is the antagonist of the former. 

 This muscle lies in the angle formed by the keel and 

 body of the sternum, and is attached also to the 

 coracoid, and partly to the clavicle on the angle of 

 its inner side. It passes under the coracoid, and the 

 tendon in which it terminates, passes through a hole 



