342 DIPODOMYS. 
incisors, acuminate; zygomata delicate, straight, abutting against 
tympanics, which are greatly inflated and possess a nontubular 
orifice of meatus; mastoids enormous; squamosals reduced; parietal 
triangle-shaped; interparietal small, situated between forks of occip- 
ital; bulla in contact below the basisphenoid; palate terminating 
posteriorly with a sharp median somewhat lengthened spur; external 
to this is a fossa with two small anterior foramina, and a large one 
behind pterygoids, with a hamular termination abutting the bulle; 
basioccipital narrow, acuminate, reduced, separated by a fissure for 
its entire length from the bulla; a similar fissure divides the last 
named bones from the alisphenoid and squamosal. The interorbital 
foramen is placed low down, midway on the side of the rostrum; 
incisive foramina minute slits between incisors and molars. In the 
rear of the skull the occipital bones appear as a rim to the foramen 
magnum; upper incisors sulcate, pointing backward; molars rootless; 
mandible small, thick, with a conspicuous acute lamina twisting 
obliquely outward and upward; mental foramen outside, near incisors; 
hind legs elongate; tail longer than head and body, penicillate; soles 
Fic. 65. DIPODOMYS PHILLIPSI. 
No. 5913 Am, Mus. Nat. Hist. Coll. Nat. size. 
UPPER TOOTH ROW. LOWER TOOTH ROW. 
Enlarged 7 times. Enlarged 7 times. 
