MORPHOLOGICAL REVISION 73 



"Anterior to the foramen trigemini, the brain contracts so as to have a trans- 

 verse diameter scarcely more than one-third its vertical diameter. The cast at a 

 point twice as far in advance of the cerebellar line as the fore-and-aft width of the 

 cerebellum, rises to fill the frontoparietal foramen, forming a mass which represents 

 the huge pineal sac or epiphysis. The proportions of this body are even greater 

 than they are in any of the existing Lacertilia, and it has a greater transverse diameter 

 than the middle brain inferior to it. Its posterior border is at right angles to the 

 line continued forwards from the superior border of the medulla oblongata at the 

 foramen magnum. At its posterior base a flat horizontal processs, as wide as the 

 brain at this point, extends posteriorly in a corresponding fossa of the superior 

 cranial wall. Its posterior margin occupies a transverse groove of the superior 

 wall between the superior and inferior plates. Each lateroposterior angle is pro- 

 duced, and may represent the foramen of exit of a narrow canal which appears 

 to perforate the lateral wall and issue beneath the roof of the temporal fossa. A 

 large projection of each side of the base of the epiphysial mass occupies a large 

 foramen of the lateral wall, which has the superior wall for its superior border. This 

 may only represent a vacuity of the wall, but the fossa at the posterior base of the 

 epiphysis has greater significance. What this is I am at present unable to ascertain. 



"Below the epiphysis the transverse diameter of the brain is about one-fourth 

 the vertical, not including a short inferior prominence. The latter is small and 

 conical, and is situated below the center of the epiphysis 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 triangular with the base superior. 

 It is impossible to distinguish the outlines of the cerebral hemispheres or the olfac- 

 tory 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 hemi- 

 spheres. 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 thala- 

 mus 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 hemi- 

 spheres. The reduced diameter of the hemispheres is a character of fishes and 

 Batrachia rather than of reptiles, but the thalami are also smaller than is the case 

 in Batrachia. The small, flat cerebellum is rather batrachian 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 



