NO. I 



THE WHITE RHINOCEROS HELLER 



27 



bony palate. The new teeth are much longer than wide with irregular 

 anterior and posterior borders. As they are pushed forward the 

 pressure shortens and widens them so that finally when the last molar 

 has assumed its position many of the teeth have become much wider 

 than long, and have had their anterior and posterior faces leveled to 

 a straight border. The tooth row is longest at the time the last molar 

 has moved up into position and shows a slight amount of wear 

 anteriorly. From this time on the wear on the premolars reduces the 

 length so that there is a gradual reduction in the length of the series 

 as age advances. 



It has not been found practicable to determine size differences in 

 individual teeth in different individuals, or for that matter, of the two 

 races here considered. The great changes taking place in the size of 

 the individual teeth due to wear make exact correlation impossible. 

 The first upper molar is the most suitable for such a comparison, 

 owing to its early eruption and long life. When first erupted this 

 tooth is much longer than wide, but as it wears down and is pushed 

 forward by the succeeding molars it gradually becomes shorter until in 

 age, when the last molar is in place, it is much wider than long. The 

 same changes take place but to a less degree in the second molar. The 

 third is more constant, but as it is only erupted in middle age it is 

 found in but a small proportion of skulls. This last molar may be 

 considered virtually a " wisdom " tooth. Curiously enough, no rhi- 

 noceros skull has been found in which the last molar shows any 

 extensive wear such as would indicate extreme old age. In Elephas 

 and Hippopotamus this condition of extreme wear is occasionally 

 found and apparently indicates that these animals sometimes outlive 

 their teeth and die of starvation. It is, however, doubtful if such a 

 fate ever overtakes a rhinoceros. 



In the mandible there are likewise four milk molars, but the first is 

 not replaced in the permanent series. The first is much more 

 delayed than in the upper series. It does not erupt until the three milk 

 molars which follow it have undergone a considerable amount of 

 wear. This is well shown in the mandible of a half-grown calf, 

 number 164588. The tooth, however, is lost early, disappearing about 

 the time the last molar begins to break through the maxillary bone. 

 The first milk molar has a simple narrow crest with very little of the 

 crescent development seen in .the posterior teeth. The milk molars 

 show a simple crown formation composed of two crests, the protolo- 

 phid and metalophid, with their valleys directed inward. The ends 

 of the protolophid unite early to form the pre-fossette. Later the tip 



