xxiii. 8 NEW WORLD MONKEYS 621 



apparatus, though smaller than in lemurs, is larger than in Old World 

 monkeys, producing the wide separation of the nostrils, from which 

 the name platyrrhine derives. Facial vibrissae are present, but usually 

 small. In the ear the tympanic bone is a ring, fused with the petrosal, 

 but is not drawn out into a tube as it is in catarrhines, and there is a 

 large bulla, which is absent in the latter. The coecum is relatively large. 

 The reproductive system does not show the full 'anthropoid' pattern; 

 for instance, there are at most only slight signs of menstrual bleeding 

 at the end of the luteal phase of the oestrus cycle. Social life is well 



Fig. 399. Common marmoset, Callithrix. (From life.) 



developed but the sexual signalling system is probably less complicated 

 than in catarrhines. Thus the colour is seldom brilliant, and the facial 

 musculature around the mouth relatively simple. The loud voice of 

 the howler monkeys (Alouatta), which have special laryngeal sacs, is 

 used in the assertion of territorial rights by the clan. This, unlike the 

 families of most monkeys, includes several mature males as well as 

 females and young. Cooperation is ensured by a language of at least 

 nine distinct sounds with separate 'meanings'. Spider monkeys 

 (Ateles, Fig. 398) have a somewhat similar organization. 



These New World monkeys are very well adapted for arboreal life, 

 with long limbs, delicate hands, and tail for balancing or seizing. The 

 tail pad has special tactile sensitivity, with ridges like those on the 

 digits and a large representation in the cerebral cortex. The animals 

 swing along freely among the branches and may make jumps in which 

 they advance by as much as 15 ft while falling 50 ft. 



The fourteen living genera of New World monkeys are divided into 

 two families, the marmosets, Callithrix (= Hapale), being more 



