CORYPHODaN. 
201 
known among Mammalia^ and greatly exceed those of UintatJierium as 
described by Marsh, and even those of OxycRna. Their peduncle is trans¬ 
versely oval in section, and is directed horizontally forward for a distance 
about half as great as the length of the hemispheres without change of form. 
The mass then expands laterally and superiorly, rising upward on each side 
of an osseous septum, which does not divide the olfactory lobes to the 
inferior face. They are thus deeply grooved above, and finally become 
furcate near to the extremity. Posterior to this point, the inferior face rises, 
and the apices project laterally and forward from the superior part of the 
lobe. The olfactory lobes consist, then, of a massive peduncle supporting 
a grooved subconical enlargement, which is bifurcate at the apex.* 
Since the internal walls of the skull show the foramina for the exits of 
the cranial nerves, we have a sufficient basis for the determination of the 
parts of the brain. In this attempt, we are met by the difficulties which 
are inherent in the use of a cast to represent a brain. Although the fora¬ 
mina sphenoorhitale and rotundun can be readily fixed, their position is such 
as to give the point of exit of the nerviis trigeminus an unusually inferior 
position. This appears to be the case to a still greater extent in the Uinta- 
therium,-f where the lateral descending masses are at the same time not nearly 
so largely developed as in Coryphodon. The large inferior area inclosed 
between these boundaries is, then, homologous with the pons varolii^ or that 
part of the encephalon which is covered by it. Its appearance in Uinta- 
therium supports this identification, but its proportions and anterior position 
in Corypliodon depart more widely from the usual form. The two anterior 
submedian ridges of its surface faintly indicated in Uintatlierium, are 
probably the homologues of the pronounced median ribs in Corypliodon, 
which resemble a continuation of the anterior pyramids of the medidla 
oblongata. As they are not very distinctly marked in the medulla of 
Corypliodon, their identification may be uncertain, but they look like that 
portion of the anterior pyramids which is continuous with the crura cerebri, 
and which are concealed in Mammalia by the pons varolii. Their promi¬ 
nence in Corypliodon indicates that the pons is wanting in this genus, as in 
* Measurements of this brain are given in the article on Corypliodon elephantopiis. 
t See Amer. Jonrn. Sci. Arts, 1876, plate iv, p. 165. 
