THE HISTORY OF THE PRIMATES 



in typical ground shrews, and the nasal apparatus is somewhat less de- 

 veloped. Thus a good case can be made for the inclusion of the tree 

 shrews with the order Primates, but they are exceedingly primitive. They 

 are at present known only in the Oriental Region, where they are widely 

 distributed. 



Lemurs. There are two groups of lemurs: the lemuriforms, now con- 

 fined to Madagascar; and the lorisiforms, found both in Africa and in 

 Asia. They vary in size from that of a mouse to that of a small monkey. 

 They are arboreal, primitive animals, some being scarcely more advanced 

 than the tree shrews. They exhibit the basic primate character of well- 

 developed hands and feet, with opposable thumbs and great toes. The 

 snout is usually long and projecting. The ears are large and mobile, but 

 there is little mobility of facial expression. The lemurs are generally noc- 

 turnal, hence their eyes are large. 



Tarsiers. The living tarsier of the Philippines and other Oriental islands 

 is the last survivor of an old and important group of Primates which was 

 probably derived from lemuroid ancestors. The tarsier ( Tarsius spectrum) 

 is about the size of a young kitten. An exclusively nocturnal animal, its 

 eyes are immense relative to the size of its head, and they look forward, 

 thus permitting binocular vision. The snout is correspondingly reduced, 

 so that it has a monkey-like appearance. The hind legs are modified for 

 jumping, and it can leap from branch to branch with considerable accu- 

 racy. The ears are large. The tail is long and naked, except for a terminal 

 hairy segment. Although tarsiers resemble lemurs in many details, the 

 structure of the brain and of the reproductive organs is essentially 

 simian. Hence some students group them with the monkeys, anthropoids, 

 and man rather than with lemurs and tree shrews. 



Monkeys. The monkeys are generally larger than the primitive Primates 

 which have just been discussed, and they are generally diurnal. The eyes 

 are set well forward, and the nasal apparatus is reduced. Generally they 

 are arboreal, but some are largely or entirely terrestrial. They are divided 

 into two contrasting groups, both of which are quite varied. These are 

 the platyrrhine monkeys of the New World and the catarrhine monkeys 

 of the Old World. The terms refer to the character of the nasal septum, 

 which is broad in the platyrrhines and narrow in the catarrhines. But 

 there are many other features distinguishing these two groups of monkeys. 

 The platyrrhines, which are restricted to South America, have generally 

 been regarded as the more primitive. Some have prehensile tails, and 

 they are the only Primates that do. They are well typified by the spider 

 monkey (Ateles) and the capuchin monkey (Cebiis), the well-known 

 organ grinder's beggar. The catarrhines are widely distributed in the Old 

 World, and include such diverse types as the macaque ( among which is 

 the rhesus monkey of medical research), the guereza, the guenon, the 

 baboons, and the mandrills. 



The Anthropoid Apes. Of all the extant Primates, those which re- 

 semble man most closely are the anthropoid apes. There are only five 

 genera living, the gibbon of Asia, the siamang of Sumatra, the orangutan 

 of Borneo and Sumatra, and the gorilla and chimpanzee of equatorial 



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