370 UNGULATA 
Horse, where the teeth assume an extremely hypsodont form, the 
original plan is so obscured by infoldings of the enamel that it can 
only be traced with difficulty. 
At the present day the Perissodactyla are sharply differ- 
entiated into Horses, Tapirs, and Rhinoceroses, but the knowledge 
already gained of the extinct representatives of the suborder shows 
such a close alliance between these groups that it is exceedingly 
difficult to make any satisfactory classification of the whole. This 
is of course exactly what might have been expected ; and the same 
would doubtless be the case with all other groups if we knew as 
much of their past history as we do of that of the Perissodactyles. 
The detailed account of the anatomy of the Horse given in the 
sequel will afford much information as to the general structure of 
the members of the suborder. 
Family TAPIRIDE. 
Both upper and lower cheek-teeth brachydont and simply 
bilophodont; hinder premolars as complex as the molars ; last lower 
molar without third lobe; first upper cheek-tooth with a milk- 
predecessor.t Outer columns of upper molars conical. Four digits 
in the manus, and three in the pes. 
Tapirus.2—Dentition i $, ¢ 1, p 4, m 3; total 42. Of the 
upper incisors, the first and second are nearly equal, with short, 
broad crowns; the third is large and conical, considerably larger 
than the canine, which is separated from it by an interval. Lower 
incisors diminishing in size from the first to the third ; the canine, 
which is in contact with the third incisor, large and conical, working 
against (and behind) the canine-like third upper incisor. In both 
jaws there is a diastema between the canines and the commence- 
ment of the teeth of the cheek-series, which are all in contact. 
First upper premolar with a triangular crown, narrow in front 
owing to the absence of the anterior inner cusp. The other upper 
premolars and molars all formed on the same plan and of nearly 
the same size, with four roots and quadrate crowns, rather wider 
transversely than from before backwards, each having four cusps, 
connected by a pair of transverse ridges, anterior and posterior. 
The first lower premolar compressed in front ; the others composed 
of a simple pair of transverse crests, with a small anterior and 
posterior cingular ridge. 
Skull elevated and compressed. Orbit and temporal fossa 
widely continuous, there being no true postorbital process from 
the frontal bone. Anterior narial apertures very large, and extend- 
ing high on the face between the orbits; nasal bones short, elevated, 
1 See W. N. Parker, Proc. Zool. Soc. 1882, Pe 075: 
* Cuvier, Tableaw Elément, de UV Hist. Nat. p. 152 (1798) ; ex Brisson. 
