402 UNGULATA 
Family RHINOCEROTIDA. 
Although the existing members of this family are readily dis- 
tinguished from the other living representatives of the suborder 
by the simple crescentoid form assumed by the ridges of the lower 
cheek-teeth, yet it is exceedingly difficult to give a definition by 
which they can be distinguished from the Lophiodontide, from some 
members of which they are, indeed, probably derived. The outer 
columns of the upper molars (Fig. 167) are, however, so excessively 
flattened as to produce 
a continuous thick and 
nearly straight outer 
wall, which is often pro- 
duced in advance of 
the anterior transverse 
ridge ; both transverse 
ridges being but little 
curved, and intimately 
connected with the 
outer wall. The upper 
premolars are in most 
cases nearly or quite as 
complex as the molars, 
and the ridges of the 
lower cheek-teeth are 
crescentoid. The last 
lower molar has no 
third lobe. The height 
of the crowns of the 
/ cheek-teeth is variable. 
Fic. 167.—A partially worn second right upper molar of The skull is large, with 
Rhinoceros untiquitatis. Letters as in Fig. 155 (p. 875), ex- the orbit confluent with 
cept k, which indicates a prolongation of the median valley. the temporal fossa 
(After Owen.) : 
wo There are either three 
or four digits in the manus, and three in the pes. One or more 
dermal horns are attached to the fronto-nasal region of the skull 
of existing forms, but these were wanting in some of the fossil 
species. 
Lhinoceros.'—Incisors variable, reduced in ‘number, often quite 
rudimentary, and early deciduous. Upper canines absent. Molar 
series, consisting of the full number of four premolars and three 
molars above and below, all in contact and closely resembling each 
other, except the first, which is much smaller than the rest and 
often deciduous ; and the last, in which the hinder lobe is partly 
1 Linn. Syst, Nat. 12th ed. vol. i. p. 104 (1766) 
