ENDOCRANIAL CAST FROM A REPTILE 137 
and lower borders are shown, for the anterior part was enclosed 
by the cartilaginous anterior wall of the skull which was lost in 
fossilization. The process extended directly downward by a 
narrow neck which passed through a narrow notch formed by 
the approximation of the alisphenoid bones at their lower borders. 
Its posterior face lay against the basisphenoid bone, not pene- 
trating it, and its lower surface is an excavation on the upper 
surface of the posterior part of the parasphenoid. The lower 
part ot the process was enlarged and the posterior face, at least, 
extended backward at a sharp angle. The lower end terminates 
in a bifureate extension which is formed by the casts of the 
beginnings of two foramina which open outwardly and down- 
ward in an excavation on the upper surface of the parasphenoid. 
These foramina continue and terminate in deep grooves on the 
side of the basisphenoid. On the posterior face of the process 
are two small prominences which mark the position of two fora- 
mina on the lower face of the basisphenoid, evidently the openings 
for the internal carotid arteries. 
The posterior part of the depressed area mentioned above 
must also include the mesencephalic portion of the brain, but 
there is nothing to mark the presence of either optic lobes or 
optic thalami. This does not, however, suggest either their 
absence or relatively small size, for if a cast were made of the 
brain cavity of Sphenodon or of an alligator no evidence of these 
structures would appear, though they are of large size. 
Posterior to the depressed area the whole cast is curved sharply 
downward and then straightened out horizontally in the metence- 
phalic region. On the lower edges of the anterior part of this 
region there are large prominences which mark the position of 
the large foramina for the passage of the V pair of nerves. There 
is no indication in the cast of the division of this nerve into its 
parts; this must have taken place external to the cranial wall. 
Within and a little posterior to these prominences is indicated 
the position of a pair of small foramina in the floor of the skull, 
evidently the outlets for the V pair of nerves. Posterior to the 
V and at about the middle of the posterior part of the cast there 
are a pair of processes on each side, one almost directly above the 
