566 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
the posterior root of the zygoma, there is a decided depression. Another 
superficial depression of considerable size is situated between the orbits, just 
in advance of the point of greatest constriction, ‘This point of greatest con- 
striction lies considerably behind the middle of the skull; the width is there 
much less than the width of the rostrum. ‘The shape of the opening repre- 
senting the conjoined orbital and temporal fosse is that of an inequilateral 
triangle, with the shortest side antero-internal, the next postero-internal ; the 
longest, formed by the malar, being iintero-external. In adults, all the sutures 
of the top of the skull are obliterated, excepting the naso-maxillary. 
The profile view of the skull, the lower jaw being removed, exhibits the 
remarkable flatness and approximate straightness, horizontality, and parallelism 
of the upper and under outlines, to which the planes of the occiput and of a 
tangent to the incisors and euds of nasals are both perpendicular. Along the 
top of the skull there is a slight bulge in the outline of the parietals, and 
an equally slight depression over the orbits, whence the profile of the rostrum 
slopes slightly downward to the end of the nasals. The occiput is perpen- 
dicular, and appears nearly straight, though the condyles and paroccipital pro- 
cesses project a little backward, and the end of the occipital crest curves a 
little forward. The outline of the palate is nearly a continuous straight hori- 
zontal line from incisors to ends of pterygoids; behind these, the bull 
auditorie project a little downward from the general plane. The anteorbital 
foramen is not visible from the side, being hidden within the anterior projec- 
tion of the zygomatic process of the maxillary. Both anterior and posterior 
roots of the zygoma dip nearly or quite down to the level of the palate; im 
its continuity, the malar rises with a gentle arch. 
Seen from below, the skull presents, of course, substantially the same 
contour as from above; so we may at once proceed to notice the details. 
It is only in this one of the three views here described that the anteorbital 
foramina appear. These are small, simple, oval apertures not prolonged into 
canals, circumscribed by the two roots of the zygomatic process of the max- 
illary ; they are oblique to all three codrdinate planes of the skull, their long 
axes being directed upward, forward, and outward. Notwithstanding their 
small size and seemingly inconvenient position, they transmit, as usual, along 
with the nerve, a little fascicle of the masseter muscle. The incisive fora- 
mina, of moderate length, but narrow, reach nearly or quite to the maxilla- 
ries, but their sides are entirely bounded by the intermaxillaries. The septum 
