12 MAMMALIA ORDER /. PRIMATES. 



relationship as does exist is of a comparatively distant kind ; and the 

 common ancestor must have lived ages before the mammoth roamed over 

 England, since at that cfate man was as distinctly differentiated from the 

 apes as he is in the present century. Whether this " missing link " will ever 

 be found, or in what country it is most likely to have lived, are questions 

 impossible to answer ; but from the extreme rarity with which fossil remains 

 of man-like apes are found in countries where they are known to have existed 

 for long ages, and from the probability that the distributional area of the 

 aforesaid "link" was extremely limited, there is not much hope that the 

 researches of palaeontologists will ever be rewarded by such a discovery. 



From their large bodily size, coupled with that hideous caricature of the 

 human face and form characterising the more typical representatives of the 

 man-like apes, no one would have any difficulty in distinguishing these crea- 

 tures from their lower relatives. There might, however, be some hesitation 

 with regard to the long-armed gibbons, and it is, therefore, essential to point 

 out how the members of the man-like group may be distinguished as a whole 

 from other monkeys. 



Among the sub-order Anthropoidea there is an important distinction be- 

 tween the Old and New World forms. The whole of the Old World repre- 

 sentatives of this division of the order are characterised by having teeth 

 agreeing both in number and arrangement with those of man. Thus in all 

 cases in each jaw there are two pairs of incisors, a single pair of tusks, or 

 canines, and five pairs of cheek-teeth, of which the last, or " wisdom-tooth/' 

 is frequently very late in making its appearance (see fig. 5). Of these five cheek- 

 teeth the first two on each side are simpler than the three hinder ones, p.iid are 

 preceded in the infant by milk-teeth, whereas the latter have no such pre- 

 decessors. It is accordingly the custom to call the two simpler teeth 

 premolars or bicuspids, and the three more complex ones molars. If, now, 

 we examine an ordinary American monkey, we shall find six check teeth on 

 each side of both the upper and lower jaws, of which half are premolars and 

 half molars ; while in the marmosets, which constitute a second American 

 family, although the total number of cheek-teeth is the same as in the Old 

 World forms, yet the proportion is different, there being chree premolars 

 and two molars. It may, therefore, be stated that all American monkeys 

 differ from their Old World cousins in having three instead of two pairs of 

 premolar teeth, whence it may be inferred that they belong tc a lower and 

 more generalized type, there being a universal tendency throughout tho 

 higher Vertebrates to a diminution, or disappearance of the teeth with the 

 advance of specialisation. In the marmosets the loss of the last molar is 

 unique in the higher division of the order, and is, indeed, a somewhat re- 

 markable peculiarity to occur in a herbivorous Mammal, among which the 

 reduction is usually confined to the front and premolar teeth. 



As the teeth serve most readily to differentiate the Old World monkeys 

 from their American allies, so the man-like apes are sharply distinguished 

 from their, relatives by the conformation of the same organs. Thus the 

 molar teeth of the man-like apes closely resemble those of man, having the 

 angles of their crowns rounded off, and carrying on their grinding-surfaces 

 four very blunt tubercles, placed alternately to one another, as well as a 

 somewhat smaller tubercle at the hinder end. On the other hand, in the 

 lower monkeys the molar teeth are oblong in form, and carry four very 

 prominent tubercles arranged in pairs at the two extremities of each tooth, 

 and each pair being connected so as to form a couple of more or less well- 



