OF COLYMBUS TORQUATUS. 165 



which its anterior border is parallel and in apposition. It runs forwards and outwards, and 

 is inserted directly into the internal tuberosity of the humerus. 



It adducts the humerus toward the body, and also depresses it Avhen elevated. 



Latissimus dorsi. The two portions into which this muscle is divided are perfectly distinct 

 as to their origin, direction, and insertion. The anterior portion is a narrow, thin, delicate, 

 ribbon-like muscle, arising from the spines of about three vertebrae opposite the middle of 

 the scapula ; passing directly outwards, over the scapular muscles, superficial to them all, it 

 is inserted into the back part of the humerus, two inches below its head, opposite the inser- 

 tion of the deltoid, close by the insertion of the posterior slip of the same muscle. 



The posterior division of this muscle, larger than the preceding, and broad and fan-shaped 

 at its origin, arises from the last four or five dorsal vertebra? ; its fibres rapidly converge, 

 and it is inserted into the humerus close by the side of the preceding portion. 



These muscles draw the humerus directly backwards, slightly rotating it outwards. 



The scapula is connected with the spine by the two layers of muscular fibres, — the 

 trapezium and rhomboideus, — as usual in the class. The fibres of the two planes decussate 

 at right angles, in the ordinary method. 



The scrratus magnus is very small and inconspicuous, arising by three digitations only, 

 passing upwards and forwards, to its usual insertion into the apex of the scapula. 



Muscles of considerable size, the homologues of the teretes, infraspinatus and subscapularis, 

 proceed from the whole length of the scapula, below the origin of the extensor of the fore- 

 arm to their insertion into the outer and posterior aspect of the head of the humerus. 

 They rotate inward, and retroduct the humerus. 



The supraspinidus, smaller than the preceding, and quite distinct from them, arises from 

 that portion of the scapula above the origin of the extensor cubiti ; and passes as a rather 

 broad and thin muscle, to be inserted into the back of the shaft of the humerus, one and a 

 half inches below its head, by a thin tendon, fully an inch in breadth. It rotates the 

 humerus slightly outwards, and directly retroducts it. 



Deltoid. Arises just at the coraco-clavicular articulation. It is small and weak, only 

 about one and a half inches long ; it passes directly over the shoulder joint, to be inserted 

 into the distal extremity of the external humeral crest. 



Immediately over the deltoid, and lying superimposed upon it, is the origin of the extensor 

 pliccti alaris. As this muscle passes over the most elevated portion of the humeral crest, it 

 gives off a tendinous slip which is inserted into the crest, after which it passes on to its in 

 sertion into the anti-brachium and metacarpus. 



Biceps flexor cubiti. This is rather a "biped" than a " biceps " muscle; having apparently 

 but one origin, and two insertions. It arises from the tip of the coracoid ; passes as a 

 rounded tendon along the depression between the anterior tuberosity and external oblique 

 ridge of the humerus ; continues single to the end of the first third of the humerus, where 

 it divides into two fleshy bellies. The larger of these is inserted by a long round tendon 

 into the tuber radii ; the other seems lost in the fascia of the forearm; being also intimately 

 blended with the fascia over which stretches the cutaneous fold at the bend of the elbow. 



A small muscle arises from the anterior aspect of the humerus, about half an inch above 

 its condyles ; passing down mesiad of the tendon of the biceps, between it and the pronator 

 radii teres, it is inserted into the inner border of the ulna, an inch or more from its head. 

 This muscle lies more upon the forearm than upon the arm ; its whole action, however, is 

 that of a flexor of the forearm; thus being perhaps analogous to the brachialis anlicus. 



