CORYPHODON. 
199 
their proximal extremities present but a single facet, except a very small 
one at the exterior border of the second, which joins the ectocuneiform. 
Brain. —I succeeded in obtaining a complete cast of the brain-cavity 
of the CorypJiodon elepJiantopus. The hard sandstone matrix which filled it 
was removed with some difficulty, the more as its surfaces were indurated 
by a cement containing much iron oxide. The osseous walls were found 
in a good state of preservation. It was ascertained that there is a consid¬ 
erable foramen lacerum posterius, but which is not nearly of such propor¬ 
tionate size as that in the genus Tapir us. 
The form of the brain is very remarkable. Its distinguishing pecu¬ 
liarities are (1) the small size of the cerebellum; (2) the large size of the 
region of the corpora quadrigemina ; (3) the small size of the hemispheres; 
(4) the enormous size of the olfactory lobes. 
There is in the cast a strong constriction in front of the medulla oblongata 
on one side, which does not exist on the other side. It is uncertain which 
represents the true form as regards the lateral portion; but that there was a 
step-like constriction across the base of the brain at this point there is no 
doubt. The medulla is very stout, and wider than the hemispheres; it is 
depressed, and a protuberance on the inferior part of each side has tlie 
appearance of the base of the eighth pair of nerves. The region of the 
cerebellum is depressed, and does not present in the cast a distinct line 
of demarkation from the medulla. An indication of the vermis is seen in 
a low, longitudinal, median protuberance. In front of this, a transverse, 
shallow depression separates it from the middle brain. 
The region of the corpora quadrigemina is the most bulky portion of 
the brain. Superiorly it presents a large transverse tuberosity, Avith the 
lateral portions well defined, but not distinguished from the cast of the 
hemispheres on the median line. From its latero-sujDerior prominences, it 
extends downward and forward on each side, expanding laterally, and nar- 
roAving as it approaches the inferior surface. Each lateral portion is sepa¬ 
rated from the hemisphere by a deep fissure, into Avhich a prominent crest 
of the lateral cranial Avails projects. This crest commences above, nearly 
at the plane of the superior wall, and curves doAviiAvard and forward to 
beloAv the middle of the cavity which contained the hemispheres. The 
