586 Mr. C. W. Andrews on a Cast of the 



the Belgian skull. Its dimensions, however, are consider- 

 ahly smaller, and since the sutures between the bones of the 

 basis cranii are closed, it no doubt belonged to an adult 

 individual, probably of the type species, /. MantelU. 



Since this interesting fragment has been in the Museum 

 a plaster cast of the cranial cavity has been prepared, which 

 seems worthy of description, because it gives a clearer idea of 

 the form of the brain than can be gathered from the descrip- 

 tion and figures of the specimen itself. 



As Hulke remarked in the paper referred to above, the 

 form of the brain in reptiles can only be deduced approxi- 

 mately from casts of their brain-cavity, since in these animals 

 it fills that cavity less completely than in the higher verte- 

 brates, though to a greater extent than in amphibians and 

 fishes. But judging from the remarkable completeness of 

 the cranial walls in this specimen, it seems possible that the 

 brain may have been more closely invested in bone than in 

 • other reptiles, and that consequently the shape of the cast 

 may give a fairly accurate idea of its general form. 



The olfactory lobes were either very small or perhaps 

 pedunculate. The space which they, or more probably their 

 basal portion, occupied is entirely filled with ironstone, so 

 that the only trace of them in the cast is a slight angular 

 projection from the middle of the antero-ventral border of the 

 cerebral liemispheres {oL). 



The hemispheres (c) themselves are of moderate size : 

 their anterior face is abruptly truncated and is only slightly 

 convex. In vertical section the conjoined hemisplieres were 

 oval in outline, the long axis of the oval being horizontal : 

 their greatest width is immediately behind their anterior face, 

 at which point they formed prominent lateral lobes and 

 measured about 62 mm. in width. Their dorsal and ventral 

 surfaces are nearly straight and parallel in a longitudinal 

 direction. On the ventral surface about an inch behind the 

 anterior extremity there is a prominence, the optic chiasma 

 (op.c), from which diverge outwards and forwards the roots 

 of the optic nerves (II.). Immediately behind tliis and 

 arising from the floor of the thalaviencephalon is the 

 infundihulumj to the lower end of which is attached the 

 pituitary body {pit.). This, so far as can be gathered from 

 the cast of the fossa which it occupied, was relatively of very 

 large size : its general form and relations are shown in the 

 figures. Its ventral surface, which slopes obliquely downward 

 and backward, is quadrate in outline; the prominent posterior 

 angles mark the position of the foramina by which the 

 internal carotids (car.) enter the skull, while the exact form 



