PANTODONTA. 
189 
which extend inward from the cranial walls, as follows: one horizontal, 
from the supra-occipital wall; two transverse and vertical, descending from 
the superior wall, the posterior of which nearly reaches the brain-cavity. 
The dental formula is | | ^ • The incisors are not closely packed; 
the canines are of very large size, and are separated by a short diastema 
from the uninterrupted series of molars. The crowns of the incisors of both 
jaws are simple and spatuliform, somewhat expanded transversely at the 
base. The canines of the opposing series differ in form. Those of the 
upper jaw have the section of the crown triangular, in some species more, 
in others less, compressed, but with the shorter line (i. e., narrower side) 
anterior. They become much worn on the anterior face by friction with the 
posterior face of the inferior canine, assuming a convex worn surface, which 
may become wider than the other faces. There is a considerable range of 
variation in the size of the canines of both jaws, especially in those of the 
inferior series, which I suspect to be due to difference of sex. 
The premolars in both jaws differ much from the true molars. In the 
superior series they consist of an external and an internal V, the former so 
oblique in tlie transverse direction that its apex stands above the middle of 
the base of the crown, or still farther interiorly. The limbs of the inner V 
rise from the position of anterior and posterior basal cingula to the cusp at 
the apex, which stands at the interior extremity of the crown. The true 
molars differ in the presence of two external V’s, and in the greater devel¬ 
opment of the anterior limb of the inner V. The apex of the latter stands 
as a trihedral antero-internal cusp, and the antero-external ridge extends 
from it to the outer side of the crown, where it turns obliquely downward. 
It forms a broad table-like ledge, as the anterior half of the surface of the 
crown. The two external V’s are of very unequal size : on the first molar, 
the anterior is flat and angular, and not more than one-quarter as large as the 
posterior; while on the second it is a small cone at the anterior base of the 
posterior V. The third true molar differs materially from the others in having 
the posterior external angle of the base of‘the crown brought round to the 
■ middle of the posterior side. The result is that the two V’s become a trans¬ 
verse crest parallel with the elevated ridge connecting the inner cusp with the 
