288 CAPT. D. M. S. WATSON ON SKYMOURlA, 



description, the discrepancies between his account nnd mine seem 

 to be ahiiost entirely, and in all important points are entirely, 

 difi'erences of interpretation and not of structure. The only sig- 

 nificant difference is that the foramen I hold to be for the Xtli 

 nerve Williston takes to be that for the Xllth. It is undeniable 

 that it does greatly resemble a hypoglossal foramen, but in the 

 several specimens in the American Museum which show both its 

 outer opening and the suture between the exoccipital and par- 

 occipital, there is no doubt that it opens between these two bones 

 as a vagus foramen always does. The course of the Xth nerve 

 demanded by Williston's interpretation leads through the large 

 cavity, which is definitely shown by an American Museum skull, 

 which I have described and figured, to have housed the vestibule 

 of the inner ear, and passes out high up in the lateral walls of 

 the skull through a foramen which is certainly absent in certain 

 well-preserved New York material, and therefore cannot be for 

 any cranial nerve. I thus still prefer my own interpretation 

 of the structure, although for theoretical reasons I should wish 

 to see a Xllth nerve in Eryops as in so many other Labyrin- 

 thodonts. 



The brain-case and otic region of Seymouria resemble the 

 corresponding regions of a Rachitomous amphibian in the follovv- 

 ing features : — 



1. The large opening from the brain-cavity to that for the 



inner ear. 



2. The position of the inner ear in the side-wall of the skull. 



3. The way in which the irnier anterior corner of the prootic 



reaches up to the skull-roof. 



4. The extremely massive paroccipital process. 



5. The upward clirection of the paroccipital process. 



6. The presence of an occipital flange from the tabular cover- 



ing a large area of the back of the paroccipital. 



The only difi"erence of importance between the ear-region of 

 Seymouria and Rachitomous amphibia is that in the reptile the 

 fenestra ovalis lies very low down, being bounded below by the 

 basisphenoid and basioccipital along the posterior margin of the 

 tubera basisphenoidalis, whilst in the Amphibia the lower border 

 of the fenestra is formed by the parasphenoid, the basioccipital 

 at any rate never entering into its margin. 



In characters 4, 5, 6, Seymouria differs from and is obviously 

 more primitive than all other reptiles, for it is easy to derive 

 the very diverse conditions in other Cotylosaurs fi'om those in it. 



The condition of the fenestra ovalis in Seymouria is paralleled 

 amongst Cotylosauria only by the Captorhinidse, which in this 

 region present an almost identical structure. 



The conditions in such types as Diadectes and Pariasaurus 

 seem to depend on a reduction in size of the stapes and a corres- 

 ponding diminution of the fenestra which receives its proximal 



