AND CLASSIFICATION OF THE FOSSIL REPTILIA. 
191 
Part II. 
The Specimen in the Museum of the Royal College of Surgeons. 
As figured by Spener, the skull is represented as having a blunt conical snout, which 
overlaps parts of some vertebrae, so as to terminate at the junction of the centrum and 
neural arch. The extremity of the jaw for a length of 12 or 13 millims. has been 
destroyed since that figure was drawn (Plate 14), so that, though the skull, as preserved, 
is 7 centims. long, it may originally have been 1-| centime, longer. This destruction 
of the anterior end of the jaw makes it impossible to determine whether the anterior 
nares occupied a terminal position as in Crocodiles, or whether they are to be sought 
in the small ant-orbital vacuities, which we shall find situate, like the nares, in 
Ichthyosaurus. Tins uncertainty affects the interpretation of the bone which carries 
the teeth. It may be either pre-maxillary or maxillary ; but can only be maxillary 
on the hypothesis that the pre-maxillary bones are lost. But Spener’s figure gives 
no indication of the nares having been terminal, and so far is evidence against that 
condition ; and the position of the nares must be inferred from their condition in the 
animal types to which the fossil may prove to approximate. 
The skull is crushed and flattened obliquely, so as to display its left side, together 
with the roof bones of the head. It is displaced from connection with the vertebral 
column, and its hinder lateral region is covered up by the anterior cervical vertebrae, 
which obliterate the bones which would demonstrate the affinities of the animal. 
The cranial bones are all remarkably dense and thin, in harmony with the large 
medullary cavities and thin walls of the limb bones ; and this osseous condition 
approximates to that which characterises the bones of Ornithosaurs and Birds. Some 
approach to this condition is seen in the limb bones of Lacertilia, and in Crocodilia 
and Dinosauria, though some American fossils referred to the Dinosauria, such as 
Megadactylus polyzelus (Hitchcock),* have the walls of the limb bones thinner. The 
solid character of the articular ends of bones in Protorosaurus, however, would 
indicate a method of ossification by conical terminal epiphyses descending into the 
shaft, like that which characterises the Batrachia, Plesiosauria, and certain Chelonia; 
so that the evidence of affinities must be fully stated before any conclusions can be 
based upon the thinness of the cranial bones. 
The brain-cavity. —The region of the brain is seen to be very narrow from side to 
side posteriorly towards the occiput, and to widen transversely as it extends forward 
towards the orbits. Portions of the parietal and frontal bones are lost, and their 
removal shows that the cerebral hemispheres were well developed. They are convex in 
length, broad, defined anteriorly by a groove in the matrix, and rounded anteriorly as 
though the brain case were closed anteriorly by bone. The lateral compression of the 
* Cope, ‘ Trans. Am. Phil. Soc.,’ vol. xiv., Plate 13, p. 1‘22 a. 
