370 U. Ss. P, R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
distinct from the squamous. They are of considerable extent, entering into the occipital sur- 
face, and very largely into the under part of the cranium. The meatus externus is broad and 
tubular, with thin walls, its axis projecting forwards, outwards, and upwards; and it is 
embraced posteriorly by a thickened process of the squamous bone. 
The malar bone is very short; its posterior half is concealed from view from above by the 
process of the temporal ; anteriorly it is more or less enlarged, and fits into a notch of the 
zygomatic plate of the maxillary, which forms the whole anterior portion of the zygoma, and 
sends a thin plate backwards under the malar. Thus, in consequence of the forward projection 
of the temporal on the upper surface of the zygoma, and the backward projection of the maxil- 
lary on the under, the two points leave but a slight interval between them when the malar bone 
is removed. 
The bony palate of Geomys is much restricted, being really confined to a narrow space between 
the molars. This is convergent anteriorly, where it is not wider than the molars ; it is traversed 
by two deep grooves, leaving a central and two lateral ridges of nearly equal height ; the central 
one is prolonged anteriorly to the incisive foramina. A plane tangent to the surface just described 
would show a considerable interval between it and the cranium or petrous bones behind, and a 
still greater one in front, the outline of the under surface of the bone rising rapidly from the 
molars to near the incisors, and then curving a little down again. The palatine surface here is 
narrow, the cross section being truncate wedge-shaped, the outline widening above. The inter- 
maxillary suture is seen on the side of the muzzle, about its middle ; just within it is seen a deep 
depression, at the bottom of which is the anterior termination of the ante-orbital foramen ; this, 
however, does not open through the bone into the nasal cavity, as in Dipodomys. The incisive 
foramina are entirely in the intermaxillaries. The zygomatic plate of the maxillary is broad and 
oblique, standing out in a plane perpendicular to the axis of the skull (the two of opposite sides 
being nearly in the same plane) ; it is nearly plane anteriorly ; its lower margin rises rapidly from 
the alveoli of the molars to a point opposite the centre of the skull, and then curves somewhat 
downward again ; it is thickened superiorly with a flattened surface, which expands behind to 
receive in its notch the end of the malar. 5 
It has already been stated that the lower jaw is very massive ; much more so than in any 
other American rodents. There is scarcely any postero-inferior angle, this being represented by 
a compressed ridge posteriorly, commencing below the root of the last molar. The upper por- 
tion of this ridge turns off horizontally, however, and is continuous with a horizontal thickened 
process standing out perpendicularly to the side of the jaw; this represents the upper corner 
of the postero-inferior angle. The lower outline of the jaw is a nearly equable and convex 
curve throughout, mostly parallel to the inferior surface of the incisor. The condyloid has 
scarcely any neck, although rather a deep notch separates it from the coronoid process, which 
rises considerably above the level of the condyle. There is a very deep pit below the base 
of the coronoid process, and exterior to the last molar. The covering of the posterior extremity 
of the lower incisor is seen as a very prominent tubercle (larger than the condyle) which is 
situated on the outside of the jaw, and at a height about midway between the condyle and the 
horizontal, process already described. There is also an excavation or pit running along the out- 
side of the jaw, internal and anterior to this tubercle. 
The incisors, as already remarked, are of extraordinary strength and size ; more or less plane 
anteriorly ; the upper grooved, the lower perfectly smooth. A section of the teeth is wedge- 
shaped ; the base anterior. The groove in the upper incisor is either central, or central and a 
