130 E. C. CASE 



lower jaw. Viewed from below, the quadrate is seen to be a thin 

 shell which is sharply convex posteriorly, the convexity forming 

 the posterior edge described above. (The form is best appreci- 

 ated by direct comparison with that of the turtles.) The outer 

 side of this convex bone is attached to the roof bones, as described 

 above. The inner side is attached to the pterygoid. There is a 

 very considerable cavity between the upper portion of the quad- 

 rate and the roof of the skull anterior to it. There was no trace 

 of a stapes preserved in the cavity of the skull posterior to the 

 quadrate. 



Cope has described the condition of the auditory region and 

 apparatus as follows (Cope, 1886) : 



The brain case in the Diadectidae differs from that of the Clepsydropidae 

 much as that of the Varanidae differ from those of other Lacertilia; that is, it is 

 continued between the orbits, so as to inclose the olfactory lobes of the brain 

 within osseous walls. These walls are thin, especially at the interorbital region, 

 and in the specimen the anterior extremity is so far imperfect as to leave the form 

 of the anterior fundus in doubt 



The conformation of the cranial walls requires preliminary notice. In the 

 first place, the vestibule of the ear can only have been separated from the brain 

 by a membranous septum, as is the case in the Protonopsis horrida (Menopoma) . 

 In clearing out the matrix no trace of osseous lamina could be detected on either 

 side, and the edges of the huge foramen thus produced are entire, and present no 

 broken edges. Anterior to the vestibule, the prootic bone has a small extension, 

 terminating in a vertical border. In front of this is the huge vertical foramen 

 through which issues the trigeminus nerve, which is even larger than that found 

 in the Testudinata and Crocodilidae. The anterior border of this foramen is 

 formed by the probable alisphenoid, whose posterior edge is nearly parallel with 

 the anterior border of the pro5tic, sloping forward as it descends. The basi- 

 cranial axis is thin at their union on the middle line below, and, thickening forward, 

 is excavated by a rather small conical fossa. Anterior to the fossa is a smaller 

 impressed fossa, and on either side of it each lateral wall is excavated into a shallow 

 fossa which descends toward it. The frontoparietal fontanelle is of extraordinary 

 size 



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 semicircular 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 upward and outward to 

 the fenestra ovalis. The "double fosste" above mentioned are the osseous 



