396 Hall and Wyman on 
teeth. "The nasal orifice is more quadrangular, but otherwise 
resembles that of the Castors. 
The zygomatic arches project farther from the side of the 
cranium, but are much more slender than in the Castors, es- 
pecially behind the post-orbitar process of the malar bone; 
the orbitar process of the frontal bone is small. The zygomatic 
process of the temporal is also more slender, and the groove 
or channel serving for the lodgment of the condyle of the 
lower jaw is destitute of the ridge on its outer border, which 
is so well marked in the Castors, Ondatras, and Capybaras. 
The infra-orbitar foramen presents nearly the same conforma- 
tion as in the Castors, but is provided externally with only a 
very slight projection of bone. 
The right inferior maxilla alone exists, and is in a perfect 
condition, excepting only the incisor tooth. Its length from the 
angle to the edge of the incisive alveolus is 7 inches, and its 
breadth from the top of the coronoid process vertically down- 
wards, 33 inches; all the processes are remarkably developed, 
and indicate the existence of powerful masticatory muscles ; 
inferiorly it is remarkably broad and almost flat, from 1.5 to 1.8 
inch in breadth, and terminating posteriorly in a triangular sur- 
face, the apex of which is turned inwards ; in these peculiar- 
ities it contrasts with the jaws of all existing Rodents. The 
condyloid and the coronoid processes are more nearly on the 
same level than in the Castors, the neck of the former being 
proportionally longer, and the plane of the whole of the ascend- 
ing portion of the jaw forming an angle of about 45° with the 
shaft of the bone, the condyle being turned inwards. Imme- 
diately beneath the triangular notch, which separates the con- 
dyloid from the eoronoid process, on the outer surface, there 
exists a deep fossa, which is limited inferiorly by the projec- 
tion formed by the walls of the cavity lodging the base of the 
incisor teeth. The insertion of the masseter muscle is plainly 
indicated by a very deep triangular impression, the apex ? 
which is directed forwards. 
