Cope.] ^ob [Oct. 16, 



when the cerebellar surface is placed horizontally, or in front of it, when 

 the medulla at the foramen is placed horizontally. Its significance is 

 unknown to me, as it is anterior to the position of the hypophysis. A 

 thickening of the cast on either side of its base converges to the median 

 line posterior to it. I can find no optic foramina, and believe, therefore, 

 that the optic nerves issued from the same large sinus as the trigeminus. 

 The cast diminishes in vertical diameter anterior to the inferior conical 

 process, and increases in transverse diameter of its superior surface. The 

 inferior border continues to be keel-like, so that a vertical section is trian- 

 gular with the base superior. It is impossible to distinguish the outlines 

 of the cerebral hemispheres or the olfactory lobes, both of which are 

 probably included in this part of the cast, although the latter probably 

 extended much anterior to the extremity of the brain case as preserved. 

 The form may or may not give an idea of the forms of the hemispheres. 

 In any case they were narrower than in any known reptile. 



The prominent features of this brain are then the following : The widest 

 part is at the origin of the trigeminus nerve. Both the cerebellum and 

 optic thalamus are flat and simple. The hemispheres are narrower than 

 the segments posterior to them, and of greater vertical diameter. The 

 epiphysis is enormous, and sends a process posteriorly between the tables 

 of the parietal bone. The olfactory lobes were apparently large, and had a 

 greater transverse diameter than the hemispheres. The reduced diameter 

 of the hemispheres is a character of fishes and Batrachia rather than of rep- 

 tiles, but the thalami are also smaller than is the case in Batrachia. The 

 small, flat cerebellum is rather batrachiau than reptilian. 



2. The Auditory Apparatus. 



As already remarked, the internal wall of the vestibule is not bony, so 

 that the cast of the brain cavity includes that of the vestibule also. On 

 the external wall of the latter are the orifices of the semi-circular canals. 

 These are, one double fossa at the superior anterior part of the wall ; a 

 second double one at the posterior superior part of the wall, and a single 

 orifice at the inferior posterior part of the wall. The external part of 

 the vestibule is produced upwards and outwards to the fenestra ovalis. 

 The "double fossae" above mentioned are the osseous representatives 

 of the membranous ampullae at the junction of two pairs of semicircular 

 canals. 



On sawing open the periotic bones, which here form a continuous mass, 

 the following is seen to be the direction of the semicircular canals. The 

 superior canal is horizontal. The second canal from the posterior ampulla, 

 descends forwards, and after a course a little longer than that of the hori- 

 zontal canal' turns posteriorly. The inferior canal from t lie anterior am- 

 pulla also descends, and after a shorter course than the canal last men- 

 tioned, also turns backwards and joins it, the two forming a single canal, 

 which enters the vestibule by the single posterior foramen already des- 

 cribed. The lumen of the longer perpendicular canal is much larger than 



