270 EXPLORATION OF THE CANONS OF THE COLORADO. 
Viewed from behind, the occipital surface is seen to be nearly plane and 
vertical, with some beveling of the lateral (mastoid) portions. The most 
remarkable feature is the extent of this surface which is formed by the mas 
toid. In Geomys, at any rate, the mastoids take as much part in the occipital 
surface as the occipital bone itself. The upper border of this surface is a 
nearly regular arch from one squarnosal angle to the other. The lower out 
line is likewise a curve, with its convexity downward, but its regularity is 
broken by the nick of the foramen magnum in the middle, the protuberance 
of the condyles next, similar parOccipital processes next, and after a little 
interval the mastoid processes. Barring these irregularities of detail, the 
general occipital surface is elliptical in shape. In the middle, and nicking the 
lower limb of the ellipse, is the foramen magnum, nearly all of which is ver 
tical, and consequently not foreshortened in this view. 
Viewed from below, the general contour is substantially like that pre 
sented from the opposite inspection, and we need only attend to details. 
The first feature is the incisive foramina very smail slits lying wholly in 
the intermaxillary bones, yet nearer to the molars than to the incisors, so 
great is the production of the rostrum. The palate proper,* i. e., the inter- 
molar portion, is extremely contracted, its width anteriorly being no greater 
than that of one of the molars. It widens a little backward. It is deeply 
twice furrowed, having a strong median ridge separating the furrows, and 
strong alveolar ridges on either hand. Posteriorly, there is a pair of deep 
pits extending to opposite the penultimate molars, and divided by a strong 
ridge. The palatal, plate upon which these pits are constructed reaches con 
siderably back of the molars in Geomys ; less so in Thomomys. The general 
resemblance of the parts to some Arvicolince, is strong. The pterygoids are 
thin, vertical, and somewhat circular plates, divaricating a little posteriorly, 
and abutting against the tips of the bulla ossea They appear like a bifurca 
tion of the median palatal ridge just mentioned. The post-palatal parts 
being contracted, like the palate itself, and compressed into small space, it is 
not easy to fully appreciate the conformation of the parts, and still less so to 
describe it. Moreover, the lamellar pterygoids are often broken off in care- 
* The long upward-sloping anterior part of palate is not "palate" at all. In life, it is altogether 
outside the mouth, like the superior incisors, and covered with furry skin. 
