MYOLOGY 165 



with the terminal portion of the sterno-prescapular anterior 

 portion of the small or deep pectoral. 



The supraspinatus, which in man is completely covered 

 by the trapezius, is partly visible in the superficial layer of 

 the cat, dog, pig, and horse, in the lower part of the space 

 limited by the mastoido-humeral and the trapezius. It is 

 crossed by the scapulo-trachclian. 



It is, in the ox, completely covered by these muscles, but 

 its form, notwithstanding this, is easily discerned by the 

 prominence which it produces. When it contracts, the 

 supraspinatus muscle carries the humerus into the position 

 of extension. 



Infraspinatus (Fig, 68, 20; Fig. 72, 8). — This muscle, 

 which occupies the infraspinous fossa, which, in quadrupeds, 

 is situated behind the spine of the scapula, arises from the 

 whole extent of this fossa, and in solipeds and ruminants 

 encroaches on the cartilage of prolongation. Its fibres are 

 directed downwards and forwards, to be inserted into the 

 great tuberosity of the humerus — the trochiter — below the 

 insertion of the supraspinatus. 



It is completely covered (ox and horse), or in part only 

 (cat and dog), by the portion of the deltoid which arises from 

 the spine of the scapula ; nevertheless, its presence is re- 

 vealed by the prominence which it produces. 



It is an abductor and external rotator of the humerus. 



In connection with this muscle, which, as we have just 

 pointed out, is less seen in the superficial muscular layer than 

 the supraspinatus, we will draw attention to the fact that 

 this arrangement is exactly the reverse of that which is found 

 in the human shoulder. In this latter it is the supraspinatus 

 which is not visible ; while, on the contrary, the infraspinatus 

 is uncovered in a considerable part of its extent. We 

 further notice that it is accompanied by the teres minor, and 

 that the teres major, situated inferiorly, forms with these two 

 muscles a fleshy mass which, below, ends on the superior 

 border of the great dorsal muscle. 



In quadrupeds, in which the infraspinatus is so slightly 

 visible, the teres major and minor are not found at all in the 

 superficial muscular layer. 



