MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 121 



abductor digiti quinti extends partially connected with the flexor 

 from the pisiform to the first phalanx. Senft (1907) thinks that be- 

 cause of the volar position of the abductor of the fifth digit in the 

 capuchin monkey, it is, in this case, more a flexor than an abductor. 

 The flexor of this digit goes from the flexor retinaculum to the first 

 phalanx. The lack of separation between the two muscles has also 

 been found in other specimens of Cebus (Straus, unpublished) where, 

 nevertheless, the opponens was present with a similar arrangement 

 to that I have found in Alouatta. 



The four lumbricals offer no significant differences in any of these 

 five platyrrhines. 



The contrahentes of Ateles were studied by Forster (1916b) and, 

 more recently, but in less detail by Jouffroy and Lessertisseur (1959). 

 Forster (1916b) indicated the presence of a superficial layer formed 

 by contrahens II and V arising from an aponeurotic raphe extended 

 obliquely from the base of metacarpale III to the head of the fifth. 

 The first of these two muscles was inserted on the ulnar base of the 

 first phalanx of digit II, the second on the radial base of the first 

 phalanx of digit V. He found contrahentes IV and I deep to the 

 first two, but with similar origins. Insertion of contrahens IV was on 

 the radial base of the first phalanx of digit IV, the adductor poUicis 

 on the fore end of the rudimentary metacarpale I. Jouffroy and 

 Lessertisseur (1959) describe the existence of additional transverse 

 bundles running between the heads of the metacarpals. Straus (un- 

 published) found, contrariwise to Forster (1916b), the adductor of 

 the thumb in a superficial layer together with m. contrahens V from 

 which it is ill separated by a raphe extending from the base to the 

 head of the third metacarpal. M. contrahens II is large and deep to 

 I, ending on the ulnar base of the first phalanx digit II. He did not 

 see a contrahens IV (Straus, unpublished). In his account of Brachy- 

 teles, Hill (1962) talks only of a contrahens II with insertion on the 

 radial side of digit III, but when covering the interossei he indicates 

 the presence of a preaxially located belly, the abductor indicis, inserted 

 on the medial margin of the extensor tendon of the index. The contra- 

 hentes of the woolly monkey (Robertson, 1944) are represented by a 

 large m. adductor pollicis arising from the carpus and a raphe extended 

 from the center of the hand to the fifth metacarpophalangeal articu- 

 lation. It covers a contrahens II called by Robertson (1944) tn. 

 adductor indicis proprius, which has what I regard as an anomalous 

 insertion to the ulnar side of the dorsal extensor expansion, although 

 he says that it sometimes takes place on the lateral side of the prox- 

 imal phalanx. If by "lateral" he means "radial," this attachment 

 would stiU be peculiar. There is, in addition, a muscular bundle 

 whose origin is from a central tendon on the carpus just medial to 



