1877. | 617 (obs 
brain. Superiorly it presents a large transverse tuberosity, with the lateral 
portions well defined, but not distinguished from the cast of the hemis- 
pheres on the median line. From its latero-superior prominences it ex- 
tends downwards and forwards on each side, expanding laterally and nar- 
rowing as it approaches the inferior surface. Each lateral portion is sepa- 
rated from the hemisphere by a deep fissure, into which a prominent crest 
of the lateral cranial walls projects. This crest commences above, nearly 
at the plane of the superior wall, and curves downwards and forwards to 
below the middle of the cavity which contained the hemispheres. The 
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 sphenodrbitale and retundum. The 
protuberance which occupies this fossa here, includes the base of the tri- 
geminus 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 cavities of the foramen ovale and the foramen lacerum 
posterius. Between these on the middle line, is a pair of longitudinal 
elevations divided by a median longitudinal depression. Posteriorly 
they rise from the transverse constriction of the medulla; anteriorly 
they terminate rather abruptly, the one half at a point anterior to the 
other. This assymmetry 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 an- 
terior to the foramen sphenoorbitale is a small fossa which I have not 
explored, but which is the opening of the foramen opticum. They are of 
small size, indicating a corresponding character 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 Uintatherium mirabile, according to the 
figures and description of Marsh. They are together about as wide as deep 
posteriorly, but both diameters diminish rapidly forwards, the vertical the 
most rapidly. The profile slopes downwards and forwards 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 smal} 
arteries that ramified in the dura mater. Owing to the prominence for- 
wards of the inferior part of the middle brain, but a small part of the in- 
ferior surface of the hemisphere is visible. The olfactory lobes are the 
largest known among Mammalia, and greatly exceed those of Uintatherium, 
as described by Marsh, and even those of Oryena. Their peduncle ig 
transversely oval in section, and is directed horizontally forwards for a 
' * Prof. Marsh (Amer. Journ. Sci. Arts, 1876, p. 166) states that both convolu- 
tions and a Sylvian fissure are present in Uintatherium. These assertions are 
not justified by his figures, nor by the probably similar brain of Coryphodon, 
