DOUGLASS: THE TERTIARY OF MONTANA 207 
peculiar lambdoid ridges on the roof of the cranium. These faint supratemporal 
ridges never come near each other, so there is no sagittal crest; yet there is a faint 
line, or narrow longitudinal ridge, on the middle line of the skull. The post-orbital 
constriction is extremely slight as seen from above; but is more noticeable inside the 
orbito-temporal fossa. The former position of what were probably the fronto- 
parietal sutures may be faintly distinguished. Faint lines extend in a transverse 
direction on the skull at the post-orbital constriction, but near the middle line they 
turn backward and meet, thus forming a V-shaped figure. 
The lambdoid ridges are continuous with the posterior portion of the zygoma. 
Just back of the auditory meatus they curve upward and ascend the brain-case 
vertically. Toward the top of the brain-case they trend slightly backward, and 
more so as they approach and meet each other at the upper portion of the occiput. 
These ridges are quite prominent on the sides, but become minute, low and nar- 
row, on top. Here the skull is highest and widest. 
The Occipital Region. —'This region may be said to be divided into three lobes 
or convexities 
a median inferior one, and two large lateral ones. The lateral ones 
are separated above by a thread-like median ridge continuous with the lambdoid 
ridges, and their lower portion by the median convexity. From the latter, they are 
separated by a shallow depression or concavity. The foramen magnum is large, 
The opening extends upward above the occipital condyles. 
The oceipital condyles are broad, and far apart above. The surfaces for the 
articulation with the atlas nearly meet below. Above each condyle is a small con- 
cavity. The basioccipital is partly hidden by the auditory bulle, which are large 
and codssified with the exoccipitals, squamosals and pterygoids. They are some- 
what flattened vertically — that is, they are not so nearly spherical as in some other 
mammals; though they are considerably inflated as seen from below. They are 
broadest internally, and narrow toward the external auditory meatus, which is short. 
They are three sided ; two of the sides are convex ; the anterior one is concave. 
There is a convexity on the middle of the lower surface and one on the inner border 
extending from the pterygoid backward nearly to the occipital condyle. The ptery- 
goids partly arch over the space behind the posterior nares, but leave a slit between 
them, which is widest in front. This may, perhaps, be considered as a tendency 
toward a character seen in modern Monotremes, the moving backward of the pos- 
terior narial opening. The glenoid surface is comparatively large and flat, and is 
bounded posteriorly by the auditory bulle. The palate is quite long and is longi- 
tudinally convex in the middle, with parallel convexities on each side between 
this and the alveoli. 
