278 EXPLORATION OF THE CANONS OF THE COLORADO. 
vertical plane of incisors; rostrum 
broad, parallel-sided. 
cisors; rostrum attenuated, taper 
ing. 
Parietals small, linear, remote from Parietals large right-angled triangles, 
the orbits. together as broad as the frontal, 
reaching orbits. 
Occipital of an ordinary character, Occipital reduced and of peculiar 
not attaining top of skull. shape ; a part of it mounting the 
top of the skull. 
Temporal bone, though of great ex- Temporal bone unique in its enor- 
tent, not remarkably inflate*d. mous size and inflation, being 
blown up like a bladder; the 
swollen mastoids forming most of 
the occipital plane ; the two tem 
porals larger than all the rest of 
the skull together.* 
Squamosal roofing most of the cere- Squamosal restricted to the orbit. 
bral cavity. 
Zygomata of an ordinary character, Zygomata thread -like in most of their 
with the usual connections. 
Tympanic, a contracted tube. 
extent, and greatly depressed in 
position ; the malar bone abutting 
against the tympanic. 
Tympanic, an inflated vestibule. 
Petrosals discrete from each other, Petrosals in mutual contact at their 
in contact with basi-occipital. extremities, and fissured away 
from basi-occipital. 
Mastoid excluded from roof of cere- Mastoid roofing most of cerebral 
bral cavity. cavity. 
Zygomatic process of maxillary a Zygomatic process developing into a 
plate with merely thickened upper 
border. 
shield over much of the orbital 
space. 
Palatal outline strongly ascending Palatal profile nearly straight and 
* If the sense of hearing of Dipodomys be co-ordinated with the osseous development of the auditory 
apparatus, it must be extraordinarily acute. 
