90 
OSTEOLOGICAL GALLERY. 
[Case 10.] 
[Case 11.] 
[Cases 
11 c'C 12.] 
premolar and molar teeth in one unbroken series, the posterior 
})remolars much resembling the true molars in shape and size. 
The dorsal and lumbar vertebrse together number at least twenty- 
two ; and, as in all other Ungulates, clavicles are entirely absent. 
The three existing families of this Suborder, the Rhinocerotida, 
Tapiridce, and Equidce, are sharply separated by the structure of 
their molar teeth and by the numbers of their toes ; these families 
are, however, very closely connected by numerous intermediate 
fossil forms, the majority of which have been found in North 
America. Such are the Lophiodontidce, the oldest Perissodactyles, 
from the Lower and Middle Eocene, allied to the Tapirs; and the 
Hijracodontidce, Macraucheniidce, Chalicotheriid(B^'dM\\. Palceotheriida, 
all more or less allied to Rhinoceros, but showing, the further we 
go back in time, a closer relationship one to another. These various 
fossil forms are described in the Guide to the Geological Galleries, 
pp. 21-23. 
The Rhinoceroses, of which a remarkably fine series of skeletons 
is placed in the centre of the Gallery, with skulls in Case 10, are 
characterized by the thickness and solidity of their bones, by the 
structure of their molar teeth, and by the enlargement of their 
nasal bones to serve as supports for the external horns. Incisor 
teeth are entirely wanting in the adults of the African species ; 
but in the Indian there is a pair of large ones above, and 
two large and two small ones below. Of the specimens exhibited 
the most noteworthy are the skeleton of the Indian Rhinoceros 
{R. unicornis), and the two fine skulls of the White Rhinoceros 
[R. simus), by far the largest of the group, ])laced in the front of 
Case 10. 
The Ta])irs (Case 11, Divs. A-D) present almost the same 
osteological characters as their ancestors, which are found fossil 
in deposits of Upper Miocene age; they belong therefore to one of 
the oldest existing types of Mammals. Their molar teeth have two 
simple transverse crests on their crowns, very different from the 
highly com})lex enamel foldings of the teeth of Rhinoceroses and 
Horses. Their nasal bones are small; their toes four in number 
on the fore, and three on the hind feet. 
The Horses {Equidce) (Case 11, Divs. E and E, and Case 12) 
of the present day consist of animals in which the gradual loss of 
the outer digits in the feet has proceeded further than in any other 
