CHARACTERS OF THE SOUTH AMERICAN MONKEYS. 



103 



Both in Alouatta and Lagothrix the pollex is normally developed 

 for the family, being perhaps a little shorter relatively than in 

 Cehus but longer than in Cacajao. The hallux is also of normal 

 length and strength*. (Text-fig. 6, C, D, and text-fig. 7, A, B.) 



In Ateles, as is well known, the hand differs from that of other 

 genera of Oebidse, except Brachrjteles , in having the pollex func- 

 tionless and at most forming a small excrescence on the side of 

 the palm ; and it is noticeable that digits 2, 3, 4, and 5 are evenly 

 spaced as in Cehus, Callicehus, etc., and that there is no grasping 

 space between digits 2 and 3 as there is in Alouatta and Lago- 

 thrix. The hand of Ateles is therefore not derivable from the 

 type of hand seen in Lagothrix, but from the more primitive type 

 of hand seen in Cehus for example t. (Text-fig. 8, A, B.) 



Text-figure 8. 



A. Right hand of Ateles po.mscus, from below. 



B. Right foot of the same. 



The foot of Ateles is characterised by the redaction in the size 

 of the hallux, which is both shorter and weaker thun in other 

 genera, the big muscular lobe at the base, representing the 

 " ball" of the human thumb, being scarcely visibly developed. 



* la a specimen of L. infamatus the second and third digits of the foot were 

 united basallj'^ bj' a short web. Possibly this was an abnormality, since no sucli 

 variation occurred in an example of L. lagotricha, 



t The only genus of Monkeys which resembles Ateles [and Braeliyteles^ in the 

 suppression of the pollex is the Catarhine Colobus. In the latter, however, the 

 suppression of the pollex is clearl}' foreshadowed in Pithecus ( = Prenbi/tes = Semno- 

 pithecus), where it is greatly reduced. 



