18 THE ANATOMY OP THE HOBSE. 



rough surface, showing that they there take origin from the inner 

 aspect of the fascia. 



The Deltoid Muscle (scapular portion) (Plates 4 and 7). This 

 muscle was by Peroivall erroneously termed the teres minor. It is 

 not the homologue of either of the teres muscles of human anatomy, 

 but is, most clearly, the representative of that part of the deltoid 

 muscle which in man takes origin from the scapula. A linear 

 depression which traverses the muscle corresponds to an imperfect 

 division of it into an anterior and a posterior portion. It arises by its 

 anterior portion from the sca2:)ular fascia, and by its posterior portion 

 from the dorsal angle of the scapula. It is inserted into the deltoid 

 ■ (external) tubercle of the humerus. 



Action. — To adduct the humerus, and rotate it outwards. Acting 

 with the teres major, it is also a flexor of the shoulder. 



Directions. — The last-mentioned muscle should be carefully cut at 

 the level of the shoulder, and reflected upwards and downwards. This 

 will expose the divisions of the circumflex vessels and nerve, branches 

 of which will be seen entering the muscle, and it will at the same time 

 bring into view the next muscle. 



The Tbee.s Minor (Plates 7 and 8). This small muscle arises from 

 the posterior border of the scapula, from the rough lines at the lower 

 part of the infraspinous fossa, and from the small tubercle on the outer 

 rim of the glenoid cavity. Its tendon, which is crossed by a glistening 

 band of fascia, is inserted into the lower half of the ridge running 

 upwards from the deltoid tubercle to the external tuberosity. 



Action. — The same as the preceding muscle. 



The Infraspinatus (subspinatus, or postea-spinatus) (Plates 7 and 8) 

 occupies the greater part of the fossa of the same name. It arises from 

 the whole extent of the fossa, and from the inner surface of the scapular 

 fascia. It possesses two tendons of insertion, the outer of which passes 

 over the convexity of the external tuberosity, a synovial bursa being 

 interposed, and is inserted into the upper half of the ridge connecting 

 that tuberosity to the deltoid tubercle. If this tendon be cut where 

 it plays over the convexity the synovial bursa will be opened, and, 

 at the same time, the inner itisertion of the muscle into the inside 

 of the convexity will be exposed. This inner tendon is more fleshy 

 than the outer, and is in contact with the capsular ligament of the 

 shoulder. 



Action. — It adducts the humerus, and rotates it outwards. 



The SuPEASPiNATUS (antea-spinatus) (Plates 7 and 8) fills the whole 

 of the fossa of the same name, and takes origin from it as well as from 

 the scapular fascia. It is bifid inferiorly, having an inner tendon irir 

 serted into the internal tuberosity at its highest point, and an outer 

 tendon inserted into the corresponding point of the external tuberosity. 



