524 MONOGRAPHS OP NORTH AMERICAN RODENTIA. 



sutures persist plainly visible in adult life; and all the bones are remarkably 

 thin and papery. 



Viewed in profile, the skull shows notable features. The highest point 

 is over the orbits, where the frontal and parietals are seen to be swollen; 

 thence the superior outline sweeps gently down to the occiput, and in the 

 other direction proceeds in a nearly straight — if anything, slightly concave — 

 line to the tip of the snout. The great projection of the nasals beyond the 

 intermaxillaries is well shown. The incisors in profile are seen to curve far 

 backward as well as downward. The palatal outline is nearly straight, and 

 declivous from before backward. Behind the palate, a small pterygoid hook 

 is seen ; but beyond this the whole outline is the inflated portions of the tem- 

 poral bone hiding everything else. On the side of the rostrum midway, there 

 is a large circular foramen, low down, but little above the palatal level ;. this 

 is the orifice corresponding to the "anteorbital" foramen, here singularly dis- 

 placed. From its fellow of the opposite side, it is only separated by a very 

 thin vertical septum, apparently ethmoidal. This delicate partition, being 

 often broken through in prepared skulls, has occasioned the statement of the 

 intercommunication of the two foramina. But I find the septum complete 

 and intact in some specimens, and although a vacuity may very possibly nat- 

 urally occur, such does not appear to be the rule. The orbit appears as a 

 subcircular fossa, largely roofed over in front by the thin expanded zygomatic 

 plate of the maxillary, and bounded below by the malar. Independently of 

 its laminar maxillary portion, the zygoma is a slender, straight thread down 

 to the palatal level, and abutting behind against the tympanic. The actual 

 suture is squamosal, of course, but there is a curious appearance of connection 

 with one of the otic bones. In the general inflation of the posterior portion 

 of the skull appears the large orifice of the meatus auditorius — a simple cir- 

 cular opening in the bullous mass. 



Viewed from below, the general contour is substantially the same as that 

 already noted from above; but many special parts claim attention. So great 

 is the backward obliquity of the incisors that their faces show in this view 

 with comparatively little foreshortening. The incisive foramina arc a pair of 

 contracted slits midway between the incisors and molars. The palatal sur- 

 face in advance of the molars is much compressed; that between these teeth 

 is broader and quite flat; its width posteriorly is little less than its length ; 

 it contracts somewhat anteriorly, where it is marked by a median ridge con- 



