350 Annals of the South African Museum. 



to the transverse ridge the basioccipital rises considerably so that 

 seen from below it has a deep central pit. This pit is triangular 

 in shape with its base behind and its apex in front. The base is 

 formed wholly by the basioccipital. The upper portion of the sides 

 is also formed by the basioccipital, but the larger, lower portion is 

 formed by the basisphenoid. Superiorly this pit divides into two 

 canals separated by a rod of bone which passes upwards from the 

 transverse basioccipital ridge and then turns forwards. The openings 

 to the canals are elongate vertically. Superiorly the basioccipital 

 meets the exoccipital. On the left hand side of the skull the suture 

 can be seen running from just below the top of the condyle - - the 

 exoccipital forming a very small portion of the condyle - - forwards 

 and slightly upwards to a point above the basioccipital tuber, and 

 then passing downwards so that the exoccipital forms part of the 

 lateral ridge running down to the tuber and meets the basisphenoid. 

 The exoccipital forms all the lateral border of the foramen magnum, 

 and the two almost meet above the foramen. The foramen for the 

 Xllth nerve (hypoglossus) is single and small. 



The basisphenoid sends back two processes as supports for the 

 tubera, as mentioned above. In front of these the bone narrows 

 somewhat and then sends forward the two pterygoid apophyses. 

 At its narrowest the bone is deeply grooved in the median line. 

 The lower border of the pterygoid apophysis bends down sharply. 



Between the exoccipital and the basisphenoid on the side is a 

 small foramen, presumably that of the carotis interna. Between the 

 exoccipital and a dumb-bell shaped piece of bone forming part of 

 the side wall of the brain and seen in oblique section is another 

 foramen. The bone is probably a portion of the prootic, and the 

 foramen, which lies above and slightly in advance of the supposed 

 foramen for the carotis interna, is probably the foramen lacerum for 

 the IXth-XIth nerves. On the dorsal side of this bridge of bone 

 is a large irregular shaped opening which I take to be the fenestra 

 ovalis and the opening for the Vlllth (auditory) nerve. Anterior to 

 this and looking downwards and forwards is the large circular 

 foramen ovale for the Vth (trigeminal) nerve. 



Anterior to the foramen magnum the brain case heightens rapidly. 

 Posteriorly it is considerably constricted and above the foramen 

 ovalis the bone of the side-wall is pierced by a small circular opening, 

 probably for a blood-vessel. Anterior to this the brain-case expands 

 laterally and is bounded by the parietal above and the alisphenoid 

 on the side - - the two bones being divided by a straight horizontal 

 suture. 



