202 
COEYPHODON. 
the Reptilia. A shallow concavity of the sphenoid bone between the origins 
of the trigemini indicates the position of a pituitary body, or hypophysis. 
In profile, the brain closely resembles in form that of a Lizard, e. g.^ an 
Amiva, excepting that in the latter the cerebellum is more prominent. The 
extension" downward and forward of the middle brain, with its projection 
below the hemispheres, is common to both; but the inferior portions, at 
least, do not appear to be homologous in the two. In the Coryphodon, the 
lateral projections correspond with the exits of the trigeminus from the 
skull; in the Amiva, this part terminates in the optic tracts. The superior 
portions of the middle brain correspond in appearance and relative size 
with that of the Amiva, but a plain difficulty in identifying them in the 
two types is derived from the difference in their inferior connections. One 
result of the examination is assured, viz, that this region is no part of the 
cerebral hemispheres, and that it is entirely uncovered by them. As it is 
not the cerebellum, it stands in the position of the corpora guadrigemina, or 
perhaps of the posterior pairmore especially. As the homologies of this region 
in the vertebrate brain are' not yet determined, further attempts to identify 
this part of it in the Amhlypoda must be postponed for the present. The 
structure is in any event entirely different from that seen in any recent 
Mammalia^ or in any Mammal of a period more modern than the Eocene 
period, and one that not only entitles these animals to a position in a peculiar 
order, but also in a special division of the class, equivalent to those based 
by Professor Owen on the modifications of the structure of the brain. The 
homologies of the olfactory lobes are simple; but their extent and form 
resemble nothing known among Mammals, even far exceeding in size those 
of Uintatheriimi. On the other hand, the}^ resemble those of Reptiles, 
especially of the Lizards, but are less deeply bifurcate anteriorly than in them. 
In the Coryplwdon elepliantopus, they equal in length the middle brain and 
hemispheres together, and their .bulb equals the hemispheres in transverse 
and vertical diameter. 
The nearest approach to the form of the brain in the Amhlypoda is seen 
in that of the Arctocyon primcEvus, a Creodont which represented the Car¬ 
nivora in tlie same Lower Eocene fauna, and was actually associated with 
Coryphodon in France. This brain is described and figured by Professor 
