Skull, Brain, &c. of Diademodon. 



223 



Taken as a whole, the labyrinth is extraordinarily similar 

 to that of Omithorhynchus in all features. 



Nasal Cavity. 



The nasal cavity is best examined in two natural casts in 

 ironstone, R. 1713, the type-specimen of Nythosaurus, and 

 R. 37G7, Diademodon sp. 



Fig. 2. 



Ironstone casts of nasal cavity and parts of brain-case of Diademodon 

 (left) and Nythosaurus (right). X 1. 



To show the ridges and furrows associated with the attachment of ethmo- 

 turbinals and the olfactory lobes in Diademodon and the whole 

 brain in Nythosaurus. 



C.L. = cerebrum; Cereb. = cerebellum ; O.L. = olfactory lobes. 



In both types the nasal cavity is very large. It is dis- 

 tinctly separated from the brain- cavity behind it by a ridge 

 on the under surface of the frontal, and extends from here 

 forwards between the orbits to the nose. The under surface 

 of the frontals, nasals, and prefrontals bears a series of 

 ridges and grooves running longitudinally; these cross 

 sutures without disturbance, and are quite similar in the two 

 genera. 



There is a strong ridge down the middle line, on each side 



