54 THE MAMMALIAN ORDER PRIMATES [SECT. A 



Tail : non-prehensile. 



Nasal septum : wide (Platyrrhine). 



Tho foregoing family includes the Marmosets. 



Family II. Cebidae 1 . 



Dental formula : i, § ; c, \ ; pm, § ; m, § = 36. 



Pollex : not opposable, in some instances rudimentary or absent 2 . 



Digits : all have flat nails. 



Cheek pouches : not developed. 



Ischial callosities : not developed. 



External auditory meatus as in Hapalidae (cf. Figs. 21 and 26). 



Tail : sometimes prehensile. 



Nasal septum broad (Platyrrhine). 



This family includes among others the Howling Monkey 

 (Mycetes), Squirrel Monkey (Chrysothrix), Spider Monkey (Ateles), 

 and Capuchin Monkey (Cebus). 



It should be particularly noted that members of the two pre- 

 ceding families (Hapalidae and Cebidae) agree in the possession 

 of a wide septum and space between the nostrils. They are for 

 this reason called Platyrrhine Monkeys. Besides this character- 

 istic, other morphological features distinguish the Platyrrhine 

 apes from the other Anthropoidea, which from the possession of 

 a narrow intra-narial space and consequent downwardly directed 

 nostrils are called Catarrhine. In Craniology the term Platyrrhine 

 is also used, but there it refers to the proportions of the apertura 

 pyriformis nasi of the skull, and not to the intra-narial space of 

 the face. 



Family III. Cercopithecidae 3 . (Cf. Fig. 27.) 



Dental formula : i, -| ; c, \ ; pm, f ; m, § = 32. 

 Pollex : opposable (but in the genus Colobus not developed 

 at all). 



1 (Cebus : the Arabic word for ape.) 



2 For a striking human example of congenital absence of both thumbs (including 

 the scaphoid and greater multangular bones) see Dr Sequeira's account in the Lancet 

 (1913, Feb. 8, p. 386). 



3 (Cercopithecns : a tailed ape.) 



