A TELEOSATJR FROM THE WHITBY LIAS. 629 



rower and directed further downward and is more anterior in 

 position. The portion of the brain or cerebral region anterior to 

 this ridge, which is thus shown to extend transversely and obliquely 

 forward and outward over the brain, is about 5 centimetres from 

 the superior termination of the brain in front, as seen in the section ; 

 and different from the condition in the middle line, this upper sur- 

 face of the cerebrum now appears in this lateral position to have 

 been slightly concave in length. Its depth at the somewhat abrupt 

 anterior termination is less than 2J centimetres ; but the form of 

 the section shows that the cerebrum was here slightly wider at 

 the base than at its upper border. The depth of the cerebrum 

 increases posteriorly to 3 centimetres, so that its upper surface must 

 have been convex from side to side, since the depth decreases pn 

 passing out laterally from the middle line. At the position where 

 the pineal gland should be, the cerebrum on this section has a depth 

 of 3^^ centimetres. Behind its small limiting transverse ridge, already 

 alluded to, is the deep excavation upward for the optic lobe (o). Its 

 height from the base of the brain-case is, however, now reduced to 

 4 centimetres ; its antero-posterior extent is less than 2 centimetres ; 

 it is margined posteriorly by a strong bony mass which separates it 

 from the cerebellum. The cavity for the optic lobe is a little com- 

 pressed superiorly and directed backward ; but since it rises high 

 above the cerebrum and occurs in the position where the brain-case 

 becomes widest, the optic lobes may be inferred to be more developed 

 laterally than in the median line, and probably extend outward 

 laterally as far as the cerebrum. The bony mass, which at first 

 sight resembles a tentorium, descends for more than 3 centimetres 

 from the roof of the brain-case, so as to leave a channel less than a 

 centimetre deep between this part of the brain-cavity and the floor 

 of the brain-case. Its antero-posterior measurement is about IJ 

 centimetre, though its outline is irregular and it is rather com- 

 pressed inferiorly. As it does not extend transversely across the 

 brain it is clearly a mass bulging inward from the side of the brain- 

 case. Examined carefully it shows a long Y-shaped groove or canal 

 which is occupied by matrix. The bones lying respectively in front 

 of and behind the long stem of the Y are probably the prootic and 

 opisthotic of Professor Huxley, while the bone above would be the. 

 epiotic. In some living Crocodiles these bones extend inward into 

 the brain-case, though never to this great degree ; nor have I 

 observed any approximation to this character in the cranial cavities 

 of other Teleosaurians ; hence, as the surface of the bone is removed 

 and the margins of the groove are sharp, the diverging branches of 

 the Y (fig. 2, ?, ?') may be anterior and posterior semicircular canals. 

 The section of the cavity for the cerebellum is subquadrate, being 

 flat above and below, with the sides nearly parallel. It is 2 centi- 

 metres deep, and about 2| centimetres long. The cerebellum 

 obviously very narrow, though the transverse width of the foramen 

 magnum, which was transversely ovate, was about 3 centimetres. 



From this description it will be manifest that the brain of this 

 Teleosaur differs remarkably from that of living Crocodiles in the 



