Evolution 



groups, the American or Western and the Eastern or Old-World 

 types, each of which is definitely confined to the regions indicated 

 by the names. The Western apes (Figs. 128 and 129) are by 

 much the lower group of the two, and in fact they lead back to 

 fossil forms which cannot be definitely distinguished from the 

 Lemurs. They are a side branch of the monkey stem, but are in 

 all probability the nearest living representatives of the first of 

 our ape ancestors. They are characterised by a wide septum 

 between the nostrils, which makes the latter open in an outward 

 direction, a feature which enables them to be distinguished at 

 a glance from the other group. They have further a prehensile 

 tail, which is of much use in climbing, and generally thirty-six 



Fig. 128. — A Marmoset {Hapale jacchus). 



teeth, or four more than the Old-World group. The lowest of 



them are the well-known Marmosets, which have claws on all the 



digits except the great toe, which last has a nail. These are 



further characterised by the presence of four nipples, all other 



monkeys having only two. Correlated with this feature, the 



Marmosets normally bear two or three young at a birth, whereas 



in all other apes one is the usual number. 



The Eastern monkeys have thirty-two teeth, the same number 



as in man ; the septum between the nostrils is narrow, so that 



these open downwards and forwards ; the tail is never prehensile 



and is frequently absent. They include such well-known forms as 



the baboons, the Gibraltar ape, the sacred Hanuman of India, 



the Diana monkey (Fig. 130), and the comical-looking Nasalis 



142 



