THE MOST PRIMITIVE KNOWN REPTILE. 



271 



Laterally to this it forms a deep plate extending downwards 

 nearly to the level of the ventral surface of the basioccipital, 

 where it ends in a suture with the prootic laterally and in a free 

 margin, part of the border of the fenestra ovalis, at its inner end. 

 The upper outer part of the posterior surface is overlapped by the 

 occipital flange of the tabular. Between this region and the top 

 of the exoccipital the upper pai-t of the posterior surface is turned 

 forward so as to form a groove, the lower part of the post-temporal 

 fossa. The cranial end of the paroccipital appears to be narrow, 

 so that the inner ear is widely open to the cranial cavity in the 

 bony skull. 



Prootic. — The prootic is fused with the lateral margin of the 

 basisphenoid below and has a suture with the paroccipital 

 behind. Its lateral face, which alone is satisfactorily shown, has 



Text-figure 3. 



Q5,0c, TftB 



Ou, Pt f:b.Pt 



Seymouria hayloriensis Broili. — Occipital view of the type-skull 

 Munich A, X f . 



Refeceiice letters as before with : — F.B.Pe., facet on the pterygoid for articulation 

 with the "basipterygoid process." 



a powerful ridge running horizontally along it at about the 

 middle of its height. Below this it is concave, its lower border 

 forming part of the rim of the fenestra ovalis mesially and laterally 

 uniting with the paroccipital, the joint bones forming the massive 

 paroccipital process which in section has a V-shaped lower surface. 

 Above the ridge the prootic is essentially flat, having however 

 a deep groove leading to a foramen towards the outer end. The 

 anterior edge of the bone is damaged, but the minute foramen fqr 

 the facial nerve is just preserved. 



The endocranial end of the bone is shown to be formed by an 

 extremely thin shell. 



Dermo-sujyraoccijyital and Tabular. — The dorsal exposure of 

 these bones on the upper table of the skull has been accurately 

 described by Broili. Munich A shows their occipital aspect 

 perfectly. Each dermo-supraoccipital has a small descending 



