316 A MANUAL OF DENTAL ANATOMY. 



establish a general community of type, so that, dissimilar 

 as they at first sight appear, it is possible to derive all, or 

 almost all, the configurations of their crowns from one or 

 two comparatively simple patterns. But odontologists are 

 not yet agreed, or rather do not yet know enough of the 

 vast number of extinct Ungulates which there is reason to 

 believe once existed (of which many have lately been dis- 

 covered) to decide with certainty what the parent pattern 

 was. 



Rhinoceros. It is difficult to assign a dental formula to 

 this genus, as the incisors are variable in the different 

 species, but all agree in the absence of canines. 



9 n 4. 3 



i^c-p 1ml. 



2 l 4 3 



In the African Rhinoceros, in which the adult has no 

 incisors, the young animal has eight incisors ; other species 

 retain the incisors through life ; and it is noteworthy that 



9 



in the Indian Rhinoceros, which has i , the outer incisors 



in the upper jaw, are, as is usual, the ones that are absent, but 

 in the lower jaw it is the central incisors which are missing. 

 The first premolar, just as in the Horse, is small, has no 

 milk predecessor, and is not long retained ; the other pre- 

 molars do not markedly differ from the true molars. The 

 premolars and molar teeth, though not differing much in 

 character, increase in size from before backwards. The 

 crowns of the teeth are of squarish outline, larger on their 

 outer than their inner side, and are implanted by four roots. 

 The pattern of their grinding surfaces is very characteristic; 

 but it will be best understood by first digressing to say a 

 few words on the dentition of the Tapir. 

 Tapir. The dental formula is 



3143 



