220 Mr. D. M. S. Watson on the 



into the brain-cavity through either of these bones, but from 

 the outer side of the depressions on the lower surface of the 

 basisphenoid, which have already been described, a small canal 

 runs quite laterally and opens on the side of the basisphenoid 

 very near its lower border and below the foramen fallopii. 

 This presumably transmits a blood-vessel. 



The exoccipital opisthotic and basioccipital are not sepa- 

 rated by clear sutures. 



The suture between the basioccipital and the other bones 

 must run either through or just within the two hypoglossal 

 foramina. 



The other two bones with the fused supraoccipital form a 

 plate, pierced in the middle by the foramen magnum and 

 notched laterally by the post-temporal fossae. 



A difference in texture of the bone in the specimen of 

 Diademodon browni already described renders it probable that 

 the exoccipital is a small bone, forming a good deal of the 

 foramen magnum and extending outwards along the lower 

 and hinder border of the paroccipital process. If this is the 

 case, the outer end of that process is formed by the opisthotic 

 with a splint of pro-otic along its anterior face. 



The upper part of the occipital plate is formed by the 

 supraoccipital and the epiotics, which are no doubt fused 

 with it. 



The pro-otic is clearly separated by suture from the basi- 

 sphenoid ; it forms the whole of the anterior border of the 

 internal auditory meatus and about half the fossa sub- 

 arcuata. Its upper border has a suture with the parietal, and 

 its posterior surface is in contact with the opisthotic and 

 " supraoccipital.'" It forms the anterior part of the vesti- 

 bule and of the fenestra ovale. It is pierced by the small 

 duct for the VII. nerve. 



The relations of the membi'ane-bones sheathing these 

 cartilage-bones are as follows : — 



The interparietal is a thin film of bone covering the back 

 of the occipital plate at the top and projecting above it to 

 articulate with the parietals. 



The tabulare is a bone which was regarded in my former 

 account as part of the parietal. It sheaths both anterior 

 and posterior surfaces of the occipital plate, having a sutural 

 connection with the interparietal and extending down outside 

 the post-temporal fossa to touch the end of the opisthotic. 



The parietals are fused in the middle line; they articulate 

 behind with the interparietal, and their lateral edges have 

 a suture with the pro-otics and, to a less degree, with 

 the supraoccipital. They send a process outward along the 



