228 On the Skull, Brain, &c. of Diademodon. 



The very remarkable size of the cerebellum in Diademodon 

 is, perhaps, to be correlated with the advanced type of limb 

 found in that group, where the characters of the humerus 

 and genoid cavity suggest that the fore limb was carried 

 somewhat like that of a higher mammal, with the feet not 

 very distant from the middle line, whilst in Dicynodon and 

 other early types and also in the living Monotremes they are 

 very widely separated, and the animal's gait was certainly 

 very slow and uncertain. 



In any case the Diademodon brain suggests very strongly 

 that in mammalian ancestors the first part of the brain to be 

 specialized was the cerebellum, which is associated with the 

 coordination of muscular movements, and that the cerebrum, 

 whose function is different, was of much later development. 



This view is in strict accordance with the fact that all 

 early and primitive mammals have very large cerebella in 

 proportion to the rest of the brain, and that in later types 

 the cerebrum increases much more rapidly than the other 

 regions. 



Many of the differences between a mammal and a reptile — 

 the soft skin, the increased body-temperature, the hair and 

 all it implies, the more perfect joints in the limbs — are 

 directly connected with increased activity and precision of 

 movement, and these in turn are dependent on cerebellar 

 improvement. 



The importance of the Diademodon brain, ear, and nose 

 lies in the evidence which they afford that this change was 

 actually taking place in the Therapsids, and that it is to all 

 appearances a very gradual one and may to a large extent have 

 preceded the development of a mammalian structure. 



I wish to express my thanks to the Percy Sladen Trustees 

 and to Mr. J. Strydom, of Winnaarsbaaken, to whose 

 hospitality I am indebted for the opportunity of collecting 

 the specimen. 



Bibliography. 



Beoom K. 1911. "On the Structure of the Skull in Cynodont 



Reptiles." Proc. Zool. Soc. 1911, pp. 893-923. 

 Seeley, H. G. 1908. " Additional Evidence as to the Dentition and 



Structure of the Skull in Diademodon." Proc. Zool. Soc. 1908, 



pp. 611-617. 

 Watson, D. M. S. 191 1. " The Skull of Diademodon." Ann. & Mag. 



Nat. Hist. ser. 8, vol. viii. pp. 293-330. 



