200 
COEYPHODON. 
inferior face of the middle region of the brain is bounded laterally by the 
projecting masses above described, posteriorly by the constriction in 
front of the medulla, and anteriorly by a slight contraction marking the 
boundary of the hemispheres. Its anterior lateral angles are continued 
into a fossa of the cranium, which I did not clear of the matrix, but which 
doubtless gives exit to the foramina splienoorhitale and rotundum. The pro¬ 
tuberance which occupies this fossa, then, includes the base of the trige¬ 
minus nerve. A short distance posterior to this position, on the inferior 
side of the lateral expansion of the middle brain, is the slight projection 
which covers the united cavities of the foramen ovale and the foramen lacerum 
jposterius. Between these, on the middle line, is a longitudinal elevation 
divided by a median longitudinal depression. Posteriorly, it rises from 
the transverse constriction of the medulla; anteriorly, it terminates rather 
abruptly, the one half at a point anterior to the other. This asymmetry 
is found in the osseous basis cranii, and is not due to accident. This 
median ridge is separated by a wide shallow concavity from the lateral 
border on each side. A short distance anterior to each foramen sphenodrhitale 
is a small fossa which I have not explored, but which is the opening of the 
foramen opticum. They are o-f small size, indicating a corresponding char¬ 
acter for the optic nerve. 
The cerebral hemispheres are relatively and absolutely very small, their 
median long diameter being one-fifteenth the total length of the skull, or a 
little smaller than those of the Uintatlierium mirahile according to the figures 
and description of Marsh. They are together about as wide as deep 
posteriorly, but both diameters diminish rapidly forward, the vertical the 
most rapidly. The profile slopes downward and forward to the base of the 
broad olfactory peduncles. There are no convolutions, nor any decided 
indication of the Sylvian fissure,* but there are surface-casts of the small 
arteries that ramified in the dura mater. Owing to the prominence forward 
of the inferior part of the middle brain, but a small part of the inferior 
surface of the hemispheres is visible. The olfactory lobes are the largest 
•* Professor Marsh (Amer. Jouru. Sci. Arts, 187G, p. 166) states that both convo¬ 
lutions and a Sylvian fissure are present in Uintatlierium. These assertions are not 
justified by his figures, nor by Ihe probably similar brain of Coryphodon. 
