OF DIDELPHYS VIRGINIANA. 115 



Supraspinatus. — (Fig- 28, h.) The muscular portion fills the whole fossa to the level 

 of the spine, and bulges above the upper border of the bone. Much of the insertion into 

 the top of tlie greater tuberosity is fleshy ; the sliort, thick, tendinous part is in intimate rela- 

 tion to the joint. The muscle has the usual action. 



Infraspinatus. — (Fig. 28, I.) Larger than the preceding, in consequence of the position 

 of the scapular spine, but with the same general characters. The insertion into the lower 

 part of the great tuberosity is almost entirely fleshy, and more or less blended with that of 

 the foregoing. The muscle everts the humerus, directly counteracting the subscapularis. 

 No teres minor can be demonstrated as distinct from the rest of the fleshy mass filling the 

 infra-spinal fossa. 



Teres major. — (Fig. 28, m.) Arises fleshy from the posterior inferior angle of the scap- 

 ula, and proceeds along the lower border of the bone, in relation wath the upper border of 

 the latissimus dorsi. It is a stout, subcylindrical muscle, passing inside the scapular head 

 of the triceps, to be inserted by a short, thin ribbon-tendon into the inner or posterior edge 

 of the bicipital groove, a little below and behind (sometimes opposite) the insertion of the 

 latissimus, with the tendon of which, however, its tendon is not conjoined. It draws the 

 humerus directly backward, and to a less degree rotates it inward. 



Deltoid. — (Fig. 28, s.) Large in superficial extent, but of only moderate thickness. 

 It is thinnest along its origin and where it passes over the tuberosity of the humerus; thicker 

 along either border. It arises from nearly the whole of the scapular spine, acromion, acro- 

 mio-clavicular ligament, and outer part of the clavicle, as far as the insertion of the cleido- 

 mastoideus, fleshy from the clavicle, l)ut by a very short aponeurosis, more or less blended 

 with the fasciae over the trapezius and infraspinatus, along the rest of its extent. From this 

 wide origin fibres converge to a point, to be inserted fleshy into the prominent, roughened 

 tubercle on the anterior face of the humerus, midway between the extremities of this bone. 

 It has the usual actions and lines of traction ; its texture is rather coarser than that of 

 surrounding muscles. It covers the shoulder-joint and upper part of the humerus, and over- 

 lies, in intimate relation with, the upper part of the great pectoral on the one side, and the 

 origins of the brachialis anticus and outer humeral and scapular heads of the triceps on the 

 other. The tendons of the pectorals separate it from the biceps. 



Coraco-brachialis. — This muscle, though very small, is not by any means rudimentary. 

 It is about an inch long, tendon and all, and rather stout for its length. It arises by a 

 slender tendon from the tip of the coracoid, forms a spindle-shajied belly, lying directly on 

 the head of the humerus, from which it is separated by the tendon of the subscapularis, 

 passing across the latter, alongside the coracoid head of the biceps, to be inserted fleshy into 

 the humerus just at the origin of the inner humeral head of the triceps, of which it appears 

 almost like a direct upward prolongation. Its action must be very feeble. 



Biceps. — (Fig. 28, r.) This muscle is remarkable in several respects. It is "biped," 

 rather than bicipital ; the division of the two portions almost makes two distinct muscles ; 

 one goes to the radius, as usual, the other to the ulna. As a whole, the muscle arises from 

 the upper margin of the glenoid fossa, the tip of the coracoid, and the intervening notch. 

 While this tendon of origin is not completely separable into two parts without some lacera- 

 tion of sclerous fibre, it really consists of two differently shaped portions. But neither of 

 these parts enters the capsular ligament of the shoulder-joint ; so that it is a question 

 whether the true glenoid or " long head of the biceps " really exists ; the part that is found, 



