COUES ON GEOMYS AND THOMOMYS OSTEOLOGY. 269 
Viewed in profile, the skull shows an almost perfectly straight dorsal 
outline from the occipital protuberance to a point just in advance of the orbits. 
Here is the highest point of the skull, whence the profile of the rostrum 
slopes gently downward, ending abruptly by vertical truncation. Likewise, 
the posterior or occipital outline is straight, or nearly so, and at a right angle 
with the superior surface. Likewise, again, the inferior surface of the skull, 
in all that part lying behind the pterygoids, presents a nearly straight and 
horizontal profile, at right angles with the occipital plane. Neither bulla 
ossea nor paroccipital nor condyle is sufficiently developed to interfere with 
the straightness of outline and rectangularity which all the back part of the 
skull presents to the side view. The rest of the under outline of the skull 
consists of the palatal profile as a whole. This consists anteriorly of a deep 
(semi-oval) concavity ; there is an abrupt rise from the incisive alveolus, and 
then a long gradual curve sloping far backward and downward to the molar 
alveolus ; while the strong obliquity of set of the anterior molars protracts 
this same curve to the tips of the teeth. The molar alveolar border is very 
short, and rather oblique, being lowest behind. The enormous arched inter 
val between the incisors and molars is highly characteristic, as is also the low 
position of the molars the teeth dip below a line drawn from the tips of the 
incisors to the foramen magnum. Behind the palate, flange-like pterygoids 
slope up to the basi-occipital plane. In this view, the zygomata are seen to 
dip but slightly downward. Their point of greatest deflection lies high above 
a line drawn from the incisive alveolus to the occipital condyle in fact, even 
above a line from the end of the nasal bones to the same point ; at their low 
est point, they are still on a level with the meatus, and they scarcely dip more 
than half-way from the top of the skull to the level of the molar crowns. 
For the rest, notable points of the profile view of the skull are the small size 
and peculiar position of the "anteorbital'' foramen, here situate low down and 
far forward in the maxillary, near its antero-inferior angle ; a deep pit, but not 
perforation, behind the zygomatic plate of the maxillary ; extensive lacerate 
foramina of exit of nerves entering the orbit from the brain ; similar fissured 
vacuities between the bulla ossea and the squamosal. The foreshortened 
tubular meatus is seen in the deep recess between the posterior root of the 
zygoma and the postero-inferior angle of the squamosal. 
