860 
support the unwieldy head or to tear up the 
ground in search of food, as the hog tribe do 
with their powerful snouts. In the young 
animal this bone always consists of four sepa- 
rate pieces—a basal, two lateral, and a superior 
occipital (fig-A71, c 1, ¢ 2, c 3 :) but these soon 
become inseparably united into one mass. 
Skull of Hippopotamus. 
Letters as in Fig. 465. 
The parietal bones ( figs.465,467, 468,471, f) 
are moderately extensive, covering the superior 
and lateral portions of the skull. In the young 
animal they are always separated by a mesial 
suture, (_ Fg. 469, b,b,) but in the adult are united 
obl 
by the iteration of this suture into one 
piece, so as to appear but a single bone; a pro- 
vision, no doubt, for admitting the enormous 
force of the temporal muscles to be exerted 
without danger of divaricating the two lateral 
halves, which might otherwise be torn asunder 
at the line of junction. In the Tapir there is a 
lofty interparietal crest, giving great additional 
surface for the origin of the temporal muscles. 
PACHYDERMATA. 
Fig. 469. 
Shull of a young Boar, Sus Scrofa, shewing the osteology of the cranium and faces, ~ 
The frontal bones are of very great extent, 
and besides enclosing the anterior part of the 
cranial box, form a large proportion of the 
orbital cavity. In the young animal (fig. 469, 
a, a) they are invariably two in number, 
separated by a suture along the mesial line, 
and in the American Tapir this separation is 
permanent; but generally they become con- 
solidated at an early age, leaving no trace of — 
their original separation. 
The ethmoid is, in the Pachydermata, of very 
considerable size, ass ie to the acuteness 
of the sense of smell with which these animals 
are gifted. The cribriform plate holds a posi- 
tion exactly similar to that which it presents 
in the human subject, implanted between the 
frontal and sphenoid bones, and testifies, by 
its great extent of surface and the numerous 
foramina which pierce it, that the olfactory 
organs are highly developed. Towards the 
nasal surface, likewise, the cethmoidal cells and 
Skull of Rhinoceros. 
~~ Letters as in Fig. 465, 
