Old World monkeys. 67 



As regards the number of their teetli, all the Old World monkej^s 



and baboons agree -w-ith 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 eacli jaw. This character, as we shall subsequently see, will at once 



serve to distinguish any Old World monkey from an American monkey or mai-moset. 



The Old World monkeys and baboons may, hoM-ever, be distinguished from the 



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



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



gi'oup closely resemble those of man ; the crowns of the molai-s being relatively 



broad and surmounteil by four low main tul^ercles situated at the four corners of 



each tooth, Ijut 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 the}' will by no 



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



teeth the four tubercles at the comei-s ; but instead of these tubercles being low, 



and set obliqueh' to one another, M'ivhout 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 Afiican 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 thstinguished 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 

 Nostrils. ■ 1 T 1 



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



the nose of an Old ^^'o^•ld monkey we shall not fail to notice that the \'ertical 



partition chviiliiig one nostril from the other is com])aratively thin : this character 



afibrthng 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. Tliis application 



of terms ^all 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 monkey.s 



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, wliich are not 



