Skull, Brain, &c. 0/ Diademodon. 227 



of the cast is very distinctly divided into two smooth 

 rounded masses, which probably reproduce the olfactory 

 lobes with some accuracy; if this is so, they are relatively 

 very large, ill correlation no doubt with the large nasal 

 cavity with an elaborate series of turbinals. 



Taken as a whole, the marked features of the brain are : — 



1. The ventral position of the exits of the nerves. 



2. The very great development of the cerebellum and the 



presence of a large flocculus. 



3. The great length and narrowness of the cerebrum. 



4. The large olfactory lobes. 



5. The fact that the cerebellum fills its cavity. 



Fig. 5. 



IXXXI 



Fen/r. 



Diademodon entomophonus. Brain-case in sagittal section, with the ear 

 and front edge of the epipterygoid projected on to it. X f . 



The stippled area represents the probable area occupied bv the brain ; 

 where it rests ou an unbroken line the brain-cavity is 'floored. 



Fen.ou. = fenestra ovale; Fen.r. = fenestra rotunda 



The type-specimen of Nythosaurus larvatus gives a good 

 cast of the brain, which differs from that described above in 

 Diademodon only in being relatively large (no doubt on 

 account of its smaller size^ and in having larger olfactory 

 lobes. 



It is an interesting fact that in Dicynodon there is in one 

 specimen a very shallow depression in a position corre- 

 sponding to the fossa subarcuata in Diademodon. This 

 suggests that the tendency to a great development of the 

 cerebellum was common amongst Therapsids. 



