12 STUDIES IN COMPARATIVE ANATOIIY. 



the ulna, immediately below the liceps. The musculo-spiral 

 nerve lies along its posterior border, while the extensor carpi radi- 

 alis longior crosses it superficially. Beneath it lies a plexus of 

 large veins, just above the elbow-joint, and a large horizontal 

 branch of the brachial artery. 



C. and L.— 276-7 (s), 283, figs. 1, 2 (s) ; 284, figs. 1, 2 (s)? 



Triceps.— ThQ middle or long head (C. and L., 274-5, t, 21^-1 

 t, 283 figs. 1, 2, f', origin only 284 fig. 1 1^ ?), arises from the 

 whole axillary border of the scapula by a thick and strong 

 fleshy mass. It expands as it passes down, blends towards the 

 elbow with the external head, and is inserted with it into the 

 posterior surface of the end of the olecranon, lying superficially 

 to the remainder of the muscle, from which it is separated indis- 

 tinctly by connective tissue. The external head (C. and L., 

 274-5, t^, 276-7, t^), the stronger of the remaining two, arises 

 from the posterior surface of the humerus, reaching as high as 

 the greater tuberosity. It bridges over the musculo-spiral nerve 

 just above the external condyloid ridge, and blends with the 

 deeper surface of the middle head. The inner head (C. and L., 

 283, fig. 1, t^, 283, fig. 2, t) has a smaU pointed origin close 

 below the insertion of latissimus dorsi. It passes downwards 

 and widens out so as to occupy the whole posterior surface of 

 the bone, between the condyloid ridges, a strong bundle taking 

 origin from the external condyloid ridge. The inner head is 

 inserted anterior to the rest of the muscle into the olecranon 

 process. 



Dorso-epitrochlearis. — A thin and flat muscle, which arises 

 close to the posterior angle of the scapula on its ventral surface, 

 and from aponeurotic fibres superficial to triceps. The lower 

 part of the muscle is connected, close to its origin, with strong 

 aponeurotic fibres derived partly from latissimus dorsi, partly from 

 panniculus, and passing into the posterior border of the middle 

 head of triceps. Borso-ejntrocMearis passes down as a thin flat 

 muscle, extensively tendinous on its deeper surface, and is 

 inserted by a smaU rounded tendon into the olecranon on its 

 inner side, close to triceps, with which it partly blends. 



C. and L., 283, fig. 1 {t), fig. 2 (t f). 



Pronator radii teres. — A strong ligament, which may repre- 

 sent this muscle, springs fi^om the inner side of the internal con- 



