240 MAMMALIAN DENTITION 



the last being the predecessors of the premolars, are the less 

 specialized and exhibit what is truly an ancestral feature. 



In many respects the milk dentition differs from the perma- 

 nent set in the characters of its constituent teeth, not so greatly 

 perhaps in the incisors, but more in the canines and most of 

 all in the milk molars, often called" milk premolars, the last of 

 Avhich at least is of a pattern much more closely resembling the 

 molar teeth of the successional set than the premolars. From 

 this fact two Avidely different interpretations have been drawn, 

 one that the milk series represents the ancestral characters of 

 the dentition such as were possessed also by the permanent set 

 in earlier forerunners, the other that the milk teeth are special- 

 ized for the peculiar needs of the young animal. Both of these 

 views present elements of truth and we shall therefore ex- 

 amine them with some attention. 



It can scarcely be said that the diet of young Mammals, once 

 they are beyond the stage of suckling, differs materially from 

 that of their parents so that the 'particular needs' of the imma- 

 ture animal are not directly connected with the type of food. 

 It is however common knowledge that the facial skeleton of 

 the young animal, in contradistinction to that of the 

 adult, is relatively small in proportion to the size of the 

 skull as a whole, and this for reasons beyond the scope of our 

 present inquiry. In the childhood of all Mammalia the jaws 

 are comparatively short and the teeth themselves are absolute- 

 ly, though not necessarily, relatively smaller than in the adult. 

 Indeed it can be demonstrated readily in any series of animals 

 with a well-developed milk dentition, let us say the Anthropoid 

 Apes, avoiding as far as possible racial discrepancies, that the 

 incisors tend to be relatively smaller and the molars relatively 

 larger in the milk dentition than in the permanent. Sex dis- 

 tinctions in the canines again are not so pronounced in the milk 

 dentition and the teeth themselves are small. The same diver- 

 gences can be observed equally well in Man and for them there 

 must be some adequate explanation. In another section (page 

 268) we note that within limits those teeth nearest to the at- 



