104 MR, R. I. POCOCK ON THE EXTERNAL 



Setting aside Callimico, whicli in the structure of the hands and 

 feet falls in with the Hapalidee, the genera of Cebida?, so far as 

 known to me, may be arranged as follows by their extremities/ — 



a. PoUex suppressed and fuuctioiiless ; hallux short, with basal 



muscular lobe scarcely developed ... Ateles [and probably BracJii/teles]. 

 a'. Pol lex and hallux normally developed. 



h. Feet relatively short as compared with the hands ; a wide 

 grasping space between digits 2 and 3 of the hand. 



Alouatta, Lagothrix. 

 h'. Feet long as compared with the hands; digits 2 to 5 of the 

 hand generallj' approximately evenly spaced, space between 

 2 and 3 a little wider in Cacajao. 



c. Pads exceedingly well developed and coarsely striated Aotvs. 



c'. Pads not noticeably strongly developed and eomparativelj^ 



weaklj' striated Cehus, Callicebus, Saimiris, Cacajao. 



Tiie hands aiid feet of Ateles show an interesting resemblance 

 to those of the Orang Utan (Siviia) amongst the Anthropoid Apes. 

 In the latter the pollex and hallux are both small, the Ape 

 depending mainly for its hold upon the clutch of digits 2 to 5, 

 which form poweiful suspensory hooks. The same applies to 

 Ateles, which, like the Ape, is no jumper, but climbs by reaching 

 from bough to bough, commonly in an inverted position, aided by 

 its prehensile tail. 



Lagothrix and Alouatta with comparatively short feet and 

 highly prehensile tails also climb by reaching instead of by 

 jumping from branch to branch. The rest of the genera with 

 I'elatively longer feet jump, so far as my experience goes, to a 

 certain extent. The species of Cehus indeed, despite their pre- 

 hensile tails, are tolerably good jumpers, but the only South 

 American Monkeys which appear to rival in arboreal activity the 

 more agile Catarhine Monkeys are the Marmozets, which can 

 cover a surprising distance with a leap. 



The Tongue. 



As in Lemurs, and some other Mammals, the lower surface of 

 the tongue in Platyrhine Monkeys is provided with a lamella — the 

 frenal lamella — in close connection with the orifices of the sub- 

 lingual salivary gland. In all cases observed this lamella ends 

 distally in a pair of slender juxtaposed processes, and its free 

 lateral margin runs backwards on each side towards the base of 

 the tongue*. (Text-tig. 9.) 



I have not seen a sufficient number of specimens to establish 

 generic differences in the structure of this frenal lamella. Its 

 apparent narrowness in some cases and breadth in others may be 

 due to contraction or expansion in accordance with the mode of 

 preservation. The greatest variation was noticed in a common 

 Marmozet {Hapale jacchus). in which the edge of the lamella was 

 denticulated ; and this condition was correlated with somewhat 

 coarse beading of the edge of the tongue. In this particular 



* This lamella corresponds, I believe, to Wharton's papillae of human anatomists, 

 and not to the sublingua of the Lemurs. 



