272 EXPLORATION OF THE CANONS OF THE COLORADO. 
alveolar plate dips down between the front teeth. The maxillary ends ante 
riorly in the curve just described ; its other boundaries are obscured in adult 
life. The side is flat ; it suddenly rises in a broad, thin, zygomatic plate, flush 
above with the general level of the top of the skull, there abutting (as shown 
by a long persistent suture) both with frontal and intermaxillary. This plate 
stands away nearly at a right angle with the axis of the skull, but very oblique 
to the other two planes. It circumscribes the orbit anteriorly; is excavated 
in the lachrymal region ; its upper border is widened to a sharp-edged 
surface, and slopes gently outward, downward, and backward ; its thin under 
margin rises to nearly meet the Dipper, finishing the laminar portion, and con 
tinuing to the malar bone as an angular process. A lachrymal bone is plainly 
indicated at the upper back part of the plate, but its extent and relations are 
not appreciable. 
The frontal is much contracted, especially across the middle, having a 
somewhat hourglass-like superior outline, though both ends are angular. In 
front, it sends a rectangular median process abutting against the nasals, and 
inclosed between the intermaxillaries, and an acute lateral process on each 
side, entering a recess between intermaxillary and maxillary. These sutures 
seem persistent. Behind, the fronto-parietal and frouto-squamosal sutures 
are commonly obliterated ;. when appreciable, the bone is seen to unite with 
the extremely narrow parietals by a directly transverse straight line, and 
with the squamosals by an oblique line on each side. These sutures persist 
longer on top of the head than in the orbital region. 
The malar bone is a mere splint, reduced corncidently with the great 
extension of the zygomatic spurs of both squamosal and maxillary. It is 
somewhat clubbed anteriorly and overrides its support ; behind, it is itself 
overlapped.* 
The parietals, as already hinted, are singularly reduced in this family. 
In the skull of an old Geomys, the squamo-parietal suture is obscure or 
inappreciable, and the squamosals appear to meet each other at the above- 
described ridge on the median line; careful inspection, however, usually 
reveals a very irregular and much overlapping squamo-parietal suture, defining 
* Although the zygoma iu this family is a good, stout arch, this reduction of the malar prepares 
us for the delicate thread-like condition of the parts in the next family, Saccom$idce. 
