ART. 18 BRACHIAL PLEXOES IN PRIMATES HOWELL AND STRAUS 9 



the anterior surface of the bone as high as the prominence marking 

 the end of the deltoid ridge, continuing along the outer side of same 

 for a few millimeters. These two origins were partially separable 

 almost as far distally as the tendon. The insertion was in common 

 Avith the long biceps head by a common tendon on the ulna. 



There was no epitroclileo-ancoiieus^ but just dorsal to the region 

 where this muscle might be expected to occur there was a M. anconeus 

 intemus, which was served by the radial nerve and passed from the 

 posterior portion of the epicondyle to the olecranon. The position 

 of this slip, which is a triceps element, served in this case to dis- 

 tinguish it from a true epitrochleo-an^oneus^ originating from the 

 anterior epicondyle; but in some mammals (rodents) this topo- 

 graphical difference seems not to exist, and identification is determi- 

 nable on innervation alone. 



In addition to the specimens described above, we have examined 

 the brachial flexors of certain other primates: The Old-World 

 monkeys Pygathrtx entellus (U.S.N.M. No. 25215), Pa/pio hariiadryas 

 (Johns Hopkins Anat. No. 149), and Lasiopyga pygerythra (Johns 

 Hopkins Anat. No. 148) ; the New- World monkeys A teles geoffroyi 

 (Johns Hopkins Anat. No. 190), Alouatta seniculus (Johns Hopkins 

 Anat. No. 13), Saimiri sciweus (Johns Hopkins Anat. No. 8), Aotiis 

 zonalis (2 specimens, Johns Hopkins Anat. Nos. 237 and 244), and 

 Oediponiidas geoffroyi (Johns Hopkins Anat. No. 234) ; and the 

 lemur Perodicticus potto (Johns Hopkins Anat. No. 283). These do 

 not depart in any significant respect from the other specimens of Old 

 and New World monkeys and lemurs described, and detailed accounts 

 of them are therefore omitted. Certain arrangements in the muscula- 

 ture and nerves of these primates are, however, referred to in the 

 succeeding discussion. 



DISCUSSION 



The intrinsic musculature of the brachium comprises only the 

 so-called extensors of dorsal innervation — the triceps complex — and 

 the so-called flexors of ventral innervation served by the musculocu- 

 taneous nerve. It is only with the latter group that we are at present 

 concerned, although for convenience we have also mentioned the epi- 

 trochleo-anconeus. The latter is served by the ulnar nerve and is 

 clearly a derivative of the antibrachial flexor carpi ulnaris element, 

 although some authors have erroneously classified it with the triceps 

 group. Its fibers have secondarily migrated above the elbow or else 

 represent a primitive humeral origin of the ulnar flexor. It is not 

 clear which of these interpretations should be regarded as the more 

 probable. 



70826—31 2 



