MUSCLES OF THE SHOULDER. 



251 



At ^ is a portion of the stei'no maxillaris, or muscle common 

 Co the fore part ol'the chest and the lower jaw. 



h designates the principal portion of this muscle, extending from 

 the shoulder to the humerus, and employed in drawing this bonp 

 towards the shoulder-blade, and bendhig the whole of the limb. 



The muscle i, antea ^yinatus, is situated on the outer and 

 anterior part of the shoulder, below and behind the muscle next 

 mentioned ; and its office is to extend the lower bone of th^^ 

 shoulder on the shoulder-blade. 



The muscle j, iios,tea sjmiatus, behind the spine or ridge, 

 occupies that space of the shoulder. It draws this bone outward 

 and upward. 



At I', is a muscle common to the breast and the shoulder-blade, 

 and called the pectoralis iiarvus,. Its action, in common with 

 that of a larger muscle, seen at w, the great 'pectoral, is to draw 

 the head of the shoulder backward, and also the lower part of the 

 shoulder-blade, and to give the latter a more upright position. 



At q, is the tendon of a very important muscle, the extensor 

 longits of the arm. At r and s, are the three divisions of another 

 muscle concerned in the same office. 



1, 2 and 3 designate the places of the principal artery, nerve, 

 and vein of the leg ; 4 gives the subcutaneous vein running within 

 the arm ; and 5 the subcutaneous vein of the side of the chest. 



Fig. 36 represents the muscles on the 

 inside of the shoulder and fore-arm. a 

 is a YQYy prominent one. It is called the 

 pectoralis transversus (the muscle cross- 

 ing the breast). The use of this muscle ^ 

 is obvious and important. It binds the 

 arm to the side of the horse ; it keeps 

 the legs straight before the horse when 

 he is at speed, that the weight of the 

 body may be received on them in a di- 

 rection most easy and safe to the horse 

 and to the rider, and most advantageous 

 for the full play of all the muscles con- 

 cerned in progression. Considering the 

 unevenness of surface over which a horse 

 often passes, and the rapid turnings 

 which are sometimes necessary, these 

 muscles have enough to do ; and when 

 the animal is pushed beyond his strength, 

 and these muscles are wearied, and the 

 fore-iegs spread out, and the horse is 

 " all abroad,'" the confused and unpleas- 

 ' ant manner of going, and the sudden 

 falling-off in speed, are well known to 



