IS"".] ^-'-•^ [Cope. 



two types, is derived from tlie difference in their inferior connections. One 

 result of the examination is assured, viz. : that tliis 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 tlie 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 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 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 tlie brain. The homologies of tlie olfactory lobes are sim- 

 ple, but their extent and form resembles nothing known among mam- 

 mals, even far exceeding in size those of Uintatheviain. On the other 

 hand, they resemble those of reptiles, especially of the lizards, but are 

 less deeplj'^ bifurcate anteriorly than in tli<^m. In the Coriipliodon ele- 

 phantopus they equal in length the middle brain and liemisi)lieres to- 

 gether, and their bulb equals the liemisi)heres in transverse and vertical 

 diameter. 



The nearest approacli to the form of the brain in the Amblypoda, is 

 seen in that of the Arctoci/aw primceDus, a Creodont which represented 

 the Carnivora in the same lower Eocene fauna, and was actually asso- 

 ciated witli Goryphodon in France. This brain is described and figured 

 bj' Prof. Gervais, Nouv. Archives du Museum, vi., 1870, p. 150, PI. 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 Edentata, present the greatest resemblances, although 

 slight ones. Among these may be noticed the small and transverse cere- 

 bellum, and esi)eciall3^ 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 Goryphodon, as, e. </., in the Eutatus 

 «6</mnj, * Gervais. There is, however, nothing exposed on the superior 

 surface in tlie Edentata which appears to be the middle brain ; hence the 

 difference from the brain of the Ai/iblypoda is very considerable. 



In reviewing the evidence brought togetiier up to the present time, the 

 writer is of the opinion tliat the type of brain shown to exist in the Am- 

 blypoda, and Creodonta, is as distinct from those cliaracterizing the pri- 

 mary divisions of the Jfawi/naZiVf, 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. Tills may be called Protencephala, 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 tlie important Memoir of Gervais, already quoted, Xouv. Arch. 

 Mns., 1809, v., p. 42. 



