ABTT | Poo 8” 619 [Cope. 
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 quadrigemina, 
or perhaps the posterior pair more 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 Amblypoda must be postponed for the pres- 
ent. The structure is inany event entirely different from that scen 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 posi- 
tion in a peculiar order, but also in a special division of the class, 
even more distinct than those based by Prof. Owen on the modifications of 
the structure of the brain. The homologies of the olfactory lobes are sim- 
ple, but their extent and form resembles nothing known among mam- 
mals, even far exceeding in size those of Uintatheriwm. On the other 
hand, they resemble those of reptiles, especially of the lizards, but are 
less deeply bifurcate anteriorly than in them. In the Coryphodon ele- 
phantopus they equal in length the middle brain and hemispheres to- 
gether, and their bulb equals the hemispheres in transverse and vertical 
diameter. 
The nearest approach to the form of the brain in the Ambdlypoda, is 
seen in that of the Arctocyon primevus, a Creodont which represented 
the Carnivora in the same lower Eocene fauna, and was actually asso- 
ciated with Coryphodon in France. This brain is described and figured 
by Prof. Gervais, Nouv. Archives du Muséum, vi., 1870, p. 150, Pl. 6 f. 
4, who notices the remerkable exposure of the middle brain or corpora 
quadrigemina. Among Mammalia of later ages some of the extinct 
South American Hdentata, present the greatest resemblances, although 
slight ones. Among these may be noticed the small and transverse cere- 
bellum, and especially the lateral expansion of the region anterior to it. 
To what portion of the brain this expansion belongs, is not known, but 
it is not unlike the lateral mass in Coryphodon, as, é. g., in the Hutatus 
seguini,* Gervais. There is, however, nothing exposed on the superior 
surface in the Edentata which appears to be the middle brain ; hence the 
difference from the brain of the Amblypoda is very considerable.. 
In reviewing the evidence brought together up to the present time, the 
writer is of the opinion that the type of brain shown to exist in the Am- 
blypoda, and Creodonta, is as distinct from those characterizing the pri- 
mary divisions of the Mammalia, as they are from each other; and that 
it necessitates the establishment of a special sub-class for their recep- 
tion of at least equal rank with the groups Gyrenrephala, Lissencephala 
and Lyencephala. This may be called Protencephata, with the following 
definition: Cerebral hemispheres smooth, small, leaving not only the 
cerebellum but the middle brain exposed behind, and contracting into the 
*Figured in the important Memoir of Gervais, already quoted, Nouv, Arch. 
Mus., 1869, v., p. 42. nc . 
