86 



larly from the base to tip. They are flat at first, but toward the end 

 become somewhat vokite or scroll-like. They remain permanently dis- 

 tinct from the interiuaxillaries, and have failed in no case to show me 

 separation from each otber. 



The intermaxillaries run up on the forehead farther than the nasals — 

 to or beyond the back instead of front border of the zygomata, being 

 received in a deep emargination of the frontal. Below, similarly, they 

 run far down on the false palate, ending opposite the back end of the 

 incisive foramina. Their course around the side of the rostrum (max- 

 illoiutermaxillary suture) may usually be traced as a strongly convex 

 curve between the upper and lower points just mentioned — the most 

 forward portion of the curve lying uearly midway between zygoma 

 and incisors. The lateral surface is thrown into a curved elevation de- 

 noting the track of the incisor within. A strong alveolar plate dips 

 down between the front teeth. The maxillary ends anteriorly 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 abut- 

 ting (as shown by a long persistent suture) both with frontal and inter- 

 maxillary. This plate stands away uearly 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, down- 

 ward, and backward; its thin under margin rises to nearly meet the up- 

 per, finishing the laminar portion, and continuing 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 nnich contracted, especially across the middle, having 

 a somewhat hourglass-like superior outline, though both ends are angu- 

 lar. 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-pari- 

 etal and fronto-squamosal sutures are commonly obliterated ; when 

 appreciable, the bone is seen to unite with the extremely narrow parie- 

 tals 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 coincidently 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 the parietals externally. These are of inde- 

 terminate shape, but tend to be narrowly rectangular ; and, in Thomomys, 

 a pair of pretty regular linear narietals is usually evident. There is con- 

 stantly an interparietal — squarish or pentagonal in TJiGmomys, rather tri- 

 angular in Geomyn. 



With such state of the parietals there is a corresponding overdevelop- 

 ment of the temporal bone — especially of its squamosal element — though 



''Although the zygoma in 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, Saccomy- 

 idcB. 



