South African Fossil Reptiles and Amphibia. 



211 



The posterior part of the busisphenoid is thin, forming a plate 

 lying below the tubera basisphenoidales. Anteriorly it thickens 

 and narrows until, at the pituitary fossa, it is a deep narrow plate 

 which passes forward to be clasped ventrally between the pterygoids. 



At its posterior end the basisphenoid forms, with the basioccipital, 

 paroccipital, and prootic, a large lounded opening which is appar- 

 ently not wholly enclosed by bone, being open on its outer side. 

 The inner portion of this pit is the fenestra ovalis, which is partially 

 walled in on the outer side by an anterior process from the par- 

 occipital (opisthotic) which stretches forwards towards the suture 

 between the basisphenoid and the prootic. 



PoOT 



H-XL 



ALOPECOGNATHUS MINOR Htn. 

 FIG. 58a. Median longitudinal section showing wall of brain-case 



from within. 

 F IG . 58b. Horizontal section across right side of brain-case just 



above the condyle. 



The foramen jugulare lies on the back of the skull at the side 

 of the occipital condyle. Its upper border is formed by the ex- 

 occipital, its lower by the basioccipital and the paroccipital. The 

 inner opening for the IXth-XIth nerves lies low down on the 

 side-wall of the brain-case, and the passage between it and the 

 foramen jugulare passes backwards and slightly outwards and 

 downwards. This canal is separated from the posterior canal 

 of the vestibule by a forward and inwardly-directed thin wall 

 formed from the inner end of the paroccipital process. Behind 

 the inner foramen for the IX-XI nerves is a small foramen opening 

 into a narrow canal which pierces the basioccipital and opens 

 into the foramen jugulare. 



