160 MAMMALIAN DENTITION 



premolar and the first molar of the maxilla. Indeed such 

 anomalies as have already been touched upon are much more 

 frequent in the upper than in the lower jaw. It is variation 

 in the molar series which occurs most frequently and has at- 

 tracted greatest attention. 



Anomalies among the molars affect number and appearance. 

 Extra teeth and extra cusps are in some instances indeed inti- 

 mately related in origin but since this is not always so one 

 must carefully avoid generalizations in discussing anomalies. 



The variation in size of the last molar and its not infrequent 

 absence indicate a condition of instability in this region but 

 the fact that the last molar is smaller than the others and is 

 often lacking in the normal molar cusp formation does not 

 in itself indicate degeneration in the modern human dentition. 

 As we have already seen these features occur in fossil Man; 

 they are present also even in primitive Mammals and they seem 

 to result from there being no tooth with which it may occlude 

 behind the third molar. 



It has been shown previously that in the specialized Negro 

 race there is a marked tendency to elongation of the last lower 

 molar through exaggerated size of the hypoconulid (Fig. 56-5). 

 The same feature has been noted in the Gorilla and Orang 

 among Anthropoids and in all the most specialized of the 

 Old-World Monkeys. We are also familiar with its occurrence 

 in the purely herbivorous Marsupials and shall meet it again 

 in other orders of Mammals where it is likewise a secondary 

 adaptation. 



It is a curious and as yet unexplained fact that, whereas ex- 

 treme reduction of the last molar is more frequently observed 

 in the maxilla, actual absence of this tooth occurs more often 

 in the mandible. In many people none of the wisdom teeth 

 erupt at all. On the other hand, a fourth molar may be found 

 in either jaw (Fig. 56-0) especially in the Negro and in Melane- 

 sian races. It is also observed occasionally in the Gorilla and 

 much more frequently in the Orang in which a fifth tooth has 

 been noted in rare instances. Accessory molars are very infre- 



