pe DIVISIONS OF PERISSODACTYLES 2 
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complete one, the more modern forms as usual being the more 
deficient in numbers of teeth. 
The dorso-lumbar vertebrae are as a rule twenty-three; but 
the extinct Titanotheres are again an exception; for, at least in 
Titanotherium, there are but twenty of these vertebrae—an Artio- 
dactyle character. The femur has a third trochanter. There are 
so few recent Perissodactyles that an enumeration of the dis- 
tinguishing characters of the viscera may very probably be use- 
less for purposes of classification. But 
the living genera at any rate are to be 
separated from the living Artiodactyles 
by the invariable simplicity of the 
stomach coupled with a very large and 
sacculated caecum. The liver is simple 
and not much broken up into lobes, and 
the gall-bladder is always absent. The 
brain is well convoluted. The teats are 
in the inguinal region. The placenta in 
this group is of the diffused kind. 
The living Perissodactyles belong to 
three types only, indeed to three genera 
only (in the estimation of most), which 
are the Horses, Tapirs, and Rhinoceroses. 
But taking into account the extinct 
forms, they may be divided primarily 5,, 193,— anterior aspect of 
(according to Professor Osborn) into the — right femur of Rhinoceros 
four following groups:—(1) Titano- eee Sahat Bu ees 
g ; t, grea : 
therioidea, including but one family, f ae ares Chu 
Titanotheriidae ; (2) Hippoidea, includ- ay ‘ 
ine the families Equidae and Palaeotheriidae; (5) Tapiroidea, 
with two families, Tapiridae and Lophiodontidae ; and (4) Rhino- 
cerotoidea with families Hyracodontidae, Amynodontidae, and 
Rhinocerotidae. It is conceivable, according to the same writer, 
that the Chalicotheres (here treated of as a separate sub-order, 
Ancylopoda)-should be added to the Perissodactyle series. 
Fam. 1. Equidae.—This family, which includes the living 
Horse, Zebras, and Asses, as well as a number of extinct genera 
agreeing with those types in structure, may be defined by the 
possession of but one functional toe, the two lateral ones being mere 
splints, or but little more. The molar teeth are hypselodont, and 
