MYOLOGY 163 



In the dog and the cat it consists of two parts, one of 

 which arises from the spine of the scapula ; the other from 

 the acromion process. Thence it passes to the crest of the 

 humerus, which Hmits the musculo-spiral groove anteriorly, 

 to be attached at a point which is found, as in other quad- 

 rupeds, to be the homologue of the human deltoid impression, 

 or deltoid V, of the human humerus. 



In the ox, in which the acromion process, which is 

 very rudimentary, does not attain the level of the glenoid 

 cavity, the acromion portion is but slightly marked off 

 from that which takes its origin from the spine of the 

 scapula. 



Still, in the horse, which is completely deprived of an 

 acromion process, the deltoid muscle is correspondingly 

 divided into two parts, separated from one another by 

 superficial interstices, but of which the arrangement differs 

 from that of the portions above indicated ; one part, the 

 posterior, arises above from the superior part of the posterior 

 border, and the postero-superior angle of the scapula (exactly 

 as if, in man, certain fasciculi of the deltoid took their 

 origin from the axillary border and inferior angle of the 

 scapula) ; the other, anterior, arises from the tuberosity of 

 the spine of the same bone. The two parts, united in- 

 teriorly, proceed to be inserted into the deltoid impression 

 or infratrochiterian crest of the humerus. 



It is necessary to add that the deltoid is inserted into the 

 humerus, above the insertion of the mastoido-humeral. 



This muscle flexes and abducts the humerus, and also 

 rotates it outwards. 



With regard to the other muscles of the human shoulder, 

 subscapularis, supraspinatus, infraspinatus, teres minor and 

 teres major, they are also present in quadrupeds, but in a 

 form more elongated, as the scapula has its dimensions more 

 extended from below upwards — that is, from the glenoid 

 cavity towards the superior or spinal border. 



Subscapularis. — This muscle occupies the subscapular 

 fossa, from which it takes its origin, leaving free the superior 

 part where the surface is found, to which are attached the 

 serratus magnus and the levator anguli scapulae. It passes. 



II — 2 



