OLD WORLD MONKEYS. 67 



As regards the number of their teeth, all the Old World monkeys 

 and baboons agree with the Man-like Apes; the total number of 

 teeth being thirty-two, among which there are two premolars and three molars on 

 both sides of each jaw. This character, as we shall subsequently see, will at once 

 serve to distinguish any Old World monkey from an American monkey or marmoset. 

 The Old World monkeys and baboons may, however, be distinguished from the 

 Man-like Apes by the form of their cheek-teeth. We have, indeed, stated at the 

 beginning of the preceding chapter that the premolar and molar teeth of the latter 

 group closely resemble those of man ; the crowns of the molars being relatively 

 broad and surmounted by four low main tubercles situated at the four corners of 

 each tooth, but arranged somewhat obliquely to its long axis. We may add that 

 the last molar in the lower jaw is of the same general form as the two teeth 

 immediately in front of it. 



If, however, we take up the skull of any species of Old World monkey or 

 baboon and carefully examine its molar teeth, we shall find that they will by no 

 means accord with the foregoing description. We shall, indeed, recognise in these 

 teeth the four tubercles at the corners ; but instead of these tubercles being low, 

 and set obliquely to one another, without any connection between those forming 

 the front and hind pairs, we shall find that they are comparatively high, and are 

 placed in pairs opposite one another, while each pair is connected together by a 

 low imperfect transverse ridge. This two-ridged character of the molars, which is 

 more distinct in the lower than in the upper teeth, is therefore a readily available 

 method of distinguishing between an Old World monkey or baboon and a Man-like 

 Ape. Moreover, with the single exception of one African genus of monkeys, and 

 one Oriental species of another, the last lower tooth of all the monkeys and baboons 

 of the Old World may be distinguished from that of the Man-like Apes by having 

 a kind of projection or heel behind the second transverse ridge. 



There are, however, other characters distinctive of the present 

 group which must now be mentioned. In the first place, if we observe 

 the nose of an Old World monkey we shall not fail to notice that the vertical 

 partition dividing one nostril from the other is comparatively thin : this character 

 affording a well-marked distinction from the monkeys and marmosets of the New 

 World. We have already seen that no Man-like Ape has a tail ; but 

 there is great variation in this respect among the members of the 

 present group, some of them having exceedingly long tails, others short tails, and a 

 few no tails at all. In no instance, however, are the tails of this group endued 

 with the power of prehension, as they are in the American monkeys. Here we may 

 remark, in passing, that it has been very often considered that the term Monkey 

 should be restricted to such species as have long tails, while those with short tails 

 should be called Baboons, and those with no tails at all Apes. This application 

 of terms will not, however, hold good when put in practice ; since, if it were adopted, 

 we should have to call certain of the different species of one single genus of monkeys 

 by all the three names. 



In all the monkeys and apes of the Old World, those peculiar patches of hard 

 naked skin on the buttocks, known as callosities, which we have already mentioned 

 AS occurring in the gibbons, are invariably present. These callosities, which are not 



