MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 89 



Ashton and Oxnard (1963). Schiick (1913a) indicates that in most 

 of his specimens of Cehus and Ateles the muscle ends on the inter- 

 muscular septum and he observed a thickening of the brachial fascia 

 following the direction of the fleshy fascicles. The termination of 

 these fibrous strands is, however, not stated. According to Hill (1962), 

 the dorso-epitrochlearis merges with the intermuscular septum above 

 the epicondyle in the woolly spider monkey. In Lagothrix (Robertson, 

 1944) it appears to have the same arrangement I have described for 

 the howler. It is evident that in all these five platyrrhines the muscle 

 ends above the elbow in the fascia of the arm, which acts as an inter- 

 mediary structure between the fleshy bundles and its own attachment 

 to the medial epicondyle, the ridge, and the olecranon. 



Forearm Group 



SUPERFICIAL SERIES, RADIAL DIVISION 



M. brachioradialis: Its long and transversely flattened belly is 

 found along the preaxial margin of the forearm. Origin is by fleshy 

 fascicles from the lower third of the lateral margin of the humerus 

 and most of the supracondylar ridge (fig. 27). The medial aspect of 

 the muscle is here strongly connected to the sheaths of m. biceps 

 and the brachialis. The fibrous strands are organized as lamellae. 

 The brachioradialis runs distally covering the two radial extensors 

 of the carpus. Some of the superficial fibers of the muscle leave its 

 posterior border to reach the intermediate third of the radius by 

 following the lateral intermuscular septum. Brachioradialis becomes 

 gradually narrower untU at the distal fifth of the antebrachium its 

 fibers end on a flat tendon that has formed in the deep aspect of the 

 muscle. This structure is firmly attached to the styloid process of the 

 radius (fig. 27). The superficial aspect of brachioradialis is related to 

 the skin and to the branches of the posterior cutaneous nerve of the 

 forearm. The cephalic vein runs proximally over its anterior border. 

 The radial and musculocutaneous nerves enter the forearm after 

 running between m. brachialis and the three humeroradial muscles 

 together with the radial recurrent artery. The radial artery now 

 joins the nerve on whose medial side it runs along the deep aspect of 

 the brachioradialis as far as the lower third of the antebrachium. 

 They pass dorsally between the tendons of the two carpal extensors 

 and that of brachioradialis to reach the dorsum of the forearm for 

 their distribution to the hand. The lateral antebrachial cutaneous 

 nerve runs parallel and partially hidden by the ventral border of the 

 brachioradialis. 



Sirena (1871) regards the supinator longus (M. brachioradialis) of 

 Alouatta as in perfect harmony ^vith that of man. He therefore does 

 not take into account the rather high humeral origin of the muscle 

 in the howler. 



