310 DAVIDSON BLACK 



of the temporal bone, while caudal of this, and separated there- 

 from by a bony prominence, a second shallow fossa in the petrous 

 bone lodges a few folia of the caudal part of the crus ascendens. 

 In contrast with this the shallow subarcuate depression in Sus 

 lodges a few folia of the flocculus proper. Further, though a 

 slight subarcuate fossa occurs on the petrous bone in Bos, Equus 

 and Cervus, no true petrosal lobule can be distinguished in these 

 forms, a negative character which, as Bolk has already pointed 

 out, they share with all other modern ungulates. 



Thus the presence of a true lobulus petrosus in Oreodon is a 

 feature apparently unique among modern ungulates, while in 

 other respects the formatio vermicularis is of a generalized ungu- 

 late type. 



Relation of cerehellum to cerehriim 



The large and specialized cerebellum in Oreodon is in striking 

 contrast with the small and relatively simply arrranged neopal- 

 lium of this form and affords an excellent example of the appar- 

 ent independence of these organs during phylogeny. 



Palmer's paper on Anoplotherium {26) is unfortunately inac- 

 cessible to me but Moodie states in his annotation {22, p. 163) 

 that in Anoplotherium 'Hhe cerebellum is very large and the 

 cerebral convolutions well marked." Since this form was an 

 Eocene mafiimal it is safe to infer that the neopallium was not 

 very extensive so the disparity between that region and the 

 large cerebellum must also have been marked in Anoplotherium. 



It would seem, however, that a highly elaborated mechanism 

 for statis, sthenic and tonic muscular control, built on lines essen- 

 tially similar to the corresponding organ of modern mammals 

 could hardly have been evolved independently of the neopallial 

 efferent projection center whose action it supplements. Obvi- 

 ously the alternative suggestion is that the neopallial efferent 

 projection center must have been laid down and functionally 

 active in these early mammals, a conclusion which accords well 

 with the prominent development of the gyri bordering the coro- 

 nal sulcus (vide supra). 



