crp:odonta. 
107 
base of the crown. The enamel border is deeply emarginate at the baso 
on the inner side, as in the other species. The enamel surface is rugulose 
on all the teeth, and on the canines the rugosities are thrown into longitu¬ 
dinal shallow grooves. 
Length of the base of the last inferior molar. 0.021 
Length of the heel of the last inferior molar. 0.007 
Width of the base of the last inferior molar. 0. 011 
Elevation of the interior cusp of the same.:. 0. 017 
Elevation of the exterior cusp of the same. 0.012 
Elevation of the anterior cusp of the same. 0.012 
A third specimen presents many fragments of the cranium, including 
some molars in place in the mandible. The frontal bone is concave in 
transverse section, and its posterior part is deeply grooved as it rises to the 
base of the crista sagittalis, where its posterior suture forms a median acute 
angle directed backward. The sides of the base of the sagittal crest are 
slightly concave. The malar bone is especially thick below the postor¬ 
bital process. The premaxillary presents a marked but open groove in front 
of the canine, and the lateral ascending portion is narrow antero-posteri- 
orly and transversely. The mandibular ramus displays a large and deep 
masseteric fossa, with a well-defined inferior border. The inferior border 
of the jaw at the angle is slightly incurved. 
The interior surface of the frontal and parietal bones is represented on 
Plate XXXV, fig. 7. The frontal sinuses are of large size, expanding out¬ 
ward and backward above the outer portion of the olfactory lobes of the 
brain. The postero-intcrnal border of each is marked by six longitudinal 
fossse. Enough of the surface of the brain-cavity remains to enable me to 
determine a number of important peculiarities in the form of the brain. 
A cast of this surface is represented on Plate LXIII, fig. 5. Prom 
this it appears that the olfactory lobes were disproportionately large, 
and the hemispheres disproportionately small. The former are greatly 
expanded outward and upward; the latter were narrowed and depressed 
in front, and give no indication of overhanging even the bases of the 
olfactory peduncles, as is observed in the lowest existing Mammals. The 
olfactory lobes appear, on the contrary, to be continuous with the anterior 
extremity of the hemispheres, as in Arctoajon and in Reptiles. The rib. 
