AND CLASSIFICATION OP TITB FOSSIL REPTILIA. 
237 
The maxillary bone is flattened, oblong, and oblique in position, being inclined 
forward and downward. Tt contributes the inferior border to the narine, and supports 
the larger part of the sub-narial bone ; but may be excluded from the external margin 
of the orbit by the malar reaching back to meet the lachrymal. It is 10 centims. 
deep and nearly 20 centims. long. A shallow depression or groove runs over the 
bone, parallel to the pre-maxillary suture and 3 or 4 centimetres below it, so as to 
define a superior convex ridge. The inferior border of the bone extends for 24 centims. 
in front of the lachrymal corner of the orbit; it is rounded, and contains the base of 
the tooth, which is sheathed in bone to its fractured extremity, where it measures 
3 centims. in diameter. 
A fracture shows the root of the tooth of the same size extendinsj for 10 centims. 
through the surrounding sheath, and it probably extends nearly to the orbit. Its 
position is parallel to the suture between the pre-maxillary and maxillary, but 
6‘5 centims. behind it. It is, therefore, not in the place of the canine tooth of a 
Carnivorous Mammal, and cannot be so determined ; but, being entirely in the middle 
of the maxillary bone, presents a character only found in the lower Mammalia. 
The nasal bones are flattened above, and they extend transversely over the hinder 
part of the iiares in a pair of thickened bulbous processes, like horns. The transverse 
width over the bones is about 19 centims. They meet by a well defined median 
suture, which is 5 or 6 centims. long ; and tfle anterior margins of the frontal bones 
rise above them in a slight ridge. These straight sutures, 8 centims. long, converge 
backward, so that the nasal bones penetrate a little between the frontal bones, but to 
a less extent than the pre-maxillary bone penetrates them. The superior surface of 
each bone is convex from front to back, and concave from the median line outward 
towards the external horn. The external antero-posterior extent of the bone is about 
7 centims., and this surface is chiefly occupied with the transverse convexity of the 
nasal horn, which is 4 centims. thick, though the thickness of the bone greatly 
diminishes towards its junction with the pre-maxillary. Interiorly the nasal rests 
upon the lachrymal bone, which extends as a narrow strip into the narine, on the 
plan of Ichthyosaurus, so as to separate the nasal bone from the maxillary. A deep 
groove behind the nasal horn separates the nasal bone from the pre-frontal. 
The sub-narial bone lies within the floor of the narine. This cavity is transversely 
ovate, 0 centims. long by 2 centims. deep internally, but 4A centims. deep to the 
outer limit of the sub-narial bone ; and a centimetre below that there is a sharp ridge 
on the maxillary, which marks the lower border of the nasal aperture. The sub-narial 
bone is 5 centims. wide and 3‘.5 centims. deep, slightly concave from front to back, 
and inclined obliquely downward and outward. It is seen on both sides of the skull. 
When compared with the sub-narial bone in Pareiasaurus, this condition is interesting, 
as the bone is entirely withdrawn from the external suture on the face. And its 
position is such as to suggest that it may be the germ of the turbinal bones of the 
Mammalia. 
