ENDOCRANIAL ANATOMY OF OREODON 285 



Cerebellum. (Figs. 9, 10, 35 and 36.) The details of the exter- 

 nal configuration of the cerebellum are reproduced with remark- 

 able clearness on the endocranial surface of the skull of this 

 specimen. Figures 35 and 36 are photographs of the plaster 

 cast of this region, while figures 9 and 10 are camera lucida draw- 

 ings of the cast in which all the essential details of the cerebellar 

 morphology have been restored on the right side. The only dif- 

 ference between the details of the photographs and those of the 

 drawings lies in the deletion on the latter of the irregularities 

 caused by the temporo-parietal canal and its associated venous 

 channels and the restoration of the underlying parts. 



Reference to figures 8 and 9 renders detailed description of this 

 cast superfluous. It should, however, be noted that the lobulus 

 paramedianus' which appears to be somewhat prominent, on the 

 drawings, is in reality placed at the bottom of a depressed area,, 

 between the posteromedian and ansiform lobules. The latter 

 lobule is quite well developed and a sulcus intercuralis may be 

 identified. Of the formatio vermicularis, the flocculus is small 

 and almost wholly hidden beneath the projecting folia of the crus 

 descendens of the pars tonsiflaris. A small nonpedunculated 

 projecting process of the crus descendens occupies the well 

 marked subarcuate fossa excavated beneath the prominence cor- 

 responding to the superior semicircular canal. This appendage 

 constitutes therefore the homologue of the lobulus petrosus of 

 carnivores. 



Specimen III {figures 11 to 14 and 37 to 40). 



In this specimen a considerable part of the ventral cerebral 

 surface of the cast had been exposed to weathering action and 

 the olfactory bulbs together with a small piece of the rostral 

 part of the cerebrum had been lost prior to being picked up in 

 the field. The extent of the weathered area is indicated in the 

 figures. 



« Throughout this paper the nomenclature used in the description of cere- 

 bellar parts is that of Bolk (4). The importance of the general adoption of this 

 nomenclature has elsewhere been emphasized (-?). 



