322 



Prof. D. M. S. Watson on 



posterior surfaces are free, tlie sides being clasped by back- 

 ward projections of the prootics, 



'^Basisphenoid." — The " basisphenoid " is a massive ossifi- 

 cation which lias invaded the side-walls of , the anterior part 

 of the brain-case and extends up to the skull-roof. 



It is a massive bone whose posterior surface is convex, and 

 resembles a condyle in surface-structure ; the rounded surface 

 faces downwards and backwards towards the basioccipital, 

 but is separated from that bone by a gap of more than 1 cm. 

 The lower part of the bone in adults is massive and is 

 covered by the hinder end of the parasphenoid. 'J'he upper 

 surface, immediately above the condyle, is concave and has 

 a smooth surface, which terminates at a strong rounded ridge, 

 in front of which the bone is so deeply excavated as to consist 

 essentially of two lateral walls. The hinder end of this exca- 

 vation runs back behind the ridge, and is, without doubt, the 



Fig-. 



Ex.Oc. 



B\r.5r. 



Macropoma mantelli. The right side of the neural cranium and parietal 

 in sagittal section, x 1. 



Reference-letters as before, with : — E.Oc, basioccipital; 

 S.Oc, supraoccipital. 



pituitary fossa. The cavity becomes very narrow as it is 

 traced torvvard, its floor contracting until the nearly straight 

 side-walls meet in an acute angle. The side- wall of this 

 cavity is pierced by four large foramina, three of which pass 

 obliquely forward and outward, the fourth going dorsally. 

 A pair of very minute foramina pierce the floor of the pitui- 

 tary fossa. 



in most individuals the lower part of the basisphenoid is 

 unossified, so that it is not in contact with the parasphenoid 

 in the middle line. 



The outer surface of this sphenoidal element is mainly 



