324 ORDERS OF MAMMALIA. 



one another in points of considerable importance, some of 

 which may be briefly alluded to. 



In the first place, as regards the dentition considerable 

 differences obtain among different species of the genus. The 

 typical dental formula is — 



. 1—1 0—0 0-0 4—4 3—3 



^ or ; c ; 7:)m ; m 



1—1 0—0' 0—0'^ 4—4' 3—3 



In many species, such as the living two-horned Ehinocer- 

 oses of Africa, there are no incisor teeth at all in the fully- 

 grown animal. In other cases {e.g., in the living it. Indicus) 

 there are two incisors in the front of both the upper and the 

 lower jaw, and the lower incisors are longer and more pointed 

 than the upper. In some of the Miocene Eliinoceroses (such 

 as R. Schleiermacheri) the front of the lower jaw carries four 

 teeth, of which the two central ones are small, while the 

 outer ones are long and pointed. These tusk-like teeth are 

 generally regarded as an external pair of incisors, but they 

 are looked upon by Gervais and Gaudry as being truly 

 canines. In tlie hornless Miocene Ehinoceroses, which con- 

 stitute the o-enus Acerothermm, the condition of matters is 

 usually as just mentioned. That is to say, the lower jaw 

 carries a pair of minute central incisors and a pair of tusk- 

 like lateral incisors (canines ?) ; but the former may be 

 wanting, and in one species of the genus the front of the 

 lower jaw carries a series of eight teeth, six incisors and two 

 canines. Lastly, the Rhinoceros Sivalensis of the Siwalik 

 Hills is stated by Falconer to possess six lower incisors. 



On each side of both loM^er and upper jaws there exists in 

 the Ehinoceroses a continuous series of seven grinding teeth, 

 of which the first four are pmemolars, and the hinder three 

 are molars (fig. 626 a). The crowns of these (fig. 626 b, 

 and figs. 627 and 628) are of the Palseotherian type, there 

 being two principal transverse tracts of dentine, separated 

 by an anterior and posterior valley, not filled up with 

 cement. 



Another point in whicli tlie Ehinoceroses differ remark- 

 ably from one another is in the form and development of 

 the nasal bones, these differences being due to the absence 



