ENDOCRANIAL ANATOMY OF OREODON 289 



Cerebellum. Compared with Specimen II the tentorial groove 

 in the specimen is shallow and indistinct so that the detail of the 

 major part of the lobus anterior is obscured. In addition, the 

 endocranial surface of the skull over the dorsal aspect of this 

 region is marked by numerous irregular vascular channels and 

 minute foramina connecting these channels with diploid spaces. 

 The skull is without doubt that of a young animal, as complete 

 adaptation of the bony parts to the underlying cerebellum has 

 not yet been brought about. Notwithstanding this, the postero- 

 median lobule has attained to large size and developed the 

 characteristic S-shape of the corresponding lobule in Specunen 

 II. Judging from the manner of growth of the postero-median 

 lobule in modern forms, it is probable that in Oreodon also the 

 lobule in question did not acquire its typical S-shape before the 

 individual had reached adult dimensions. It is therefore prob- 

 able that the skull is that of a young but full grown animal. 



The detail of the arrangement of the formatio vermicularis in 

 this specimen is excellent, particularly that of the crus descendens 

 and its small but well marked lobulus petrosus. 



Specimen IV (figures 15 to 18 and 4I to 44) 



The entire endocranial cast is represented in this specimen. 

 The greatest transverse diameter of the cerebral portion is 4.6 

 cm. The maximum interpyriform diameter is 4.5 cm. The 

 maximum fronto-occipital diameter of the cerebrum is 4.6 cm. 

 and its maximum height 3.1 cm. In the cerebellar region the 

 greatest transverse diameter is 3.5 cm. and the ponto-dorsal 

 maximum height is 3.3 cm. The volume of the cerebral portion 

 of the cast is 37 cc, that of the cerebellum and brain stem being 

 15 cc. 



Brain stern arid basis cranii. (Fig. 17.) The relations of the 

 ventral surface of the olfactory tract to the tuberculum promi- 

 nence are well shown in this cast, and particularly so on the 

 right side. Here again may be seen some strand-like markings 

 resembling those already noticed in Specimen I, though not so 

 strongly developed. They are not to be confused with vascular 



