Ostt'ologij of the. I lend n/' IlattcMin, 307 



to the antorior surface of the processus jiarotlcus, and forms 

 the uj)per niart;in of tlie sulcus coluinelho auditus. 



The anterior end of the upper border is likewise produced 

 into a ])rocess, the processus anterior superior, \vhicli in tlie 

 other lizards remains very short and serves for the attach- 

 ment of the upper trabecuUi. 



The lower border unites with the basisplienoid ; its ante- 

 rior end is elongated in the shape of a shovel and forms the 

 processus anterior inferior, which is united with the processus 

 alaris of the basisplienoid. The anterior end of the bone 

 serves for the attachment of the lower cartila<^inous branch of 

 the orbitospljenoid. The posterior truncated end of the lower 

 border unites with the plate of cartilage which extends 

 between the otosphenoid, basisplienoid, paroccipital, and 

 basioccipital. The posterior free border of the otosphenoid, 

 together with the paroccipital, encloses the very large foramen 

 vestibuli seu ovale, ^n the anterior free border we find a 

 crest which is quite small, indicating the ala otos[)l)enoidea, 

 below which is situated the incisura otospheuoidea for the 

 exit of the fifth nerve (trigeminus). 



The external surface of the otosphenoid is strongly convex. 

 Upon it niay be seen standing out in relief in front and above 

 the canalis semicircularis sagittalis running towards the 

 middle, and the canalis semicircularis horizontalis running in 

 the same direction from the base of the processus posterior 

 superior. Towards the lower border, behind the origin of the 

 processus anterior inferior, we find an indication of a very 

 short crista otospheuoidea, behind which lies the foramen 

 nervis facialis. 



The inner surface forms the anterior vestibular cavity, and 

 for this purpose is strongly excavated. It consists of the 

 posterior portion, the actual vestibulum, and of the anterior, 

 much smaller, but very deep portion, the anterior ampullary 

 cavity. Into this there opens quite at the bottom, as a 

 transversely oval hole, the oriHcium ampullar canalis semi- 

 circularis sagittalis, the orificium ampuUas canalis semicir- 

 cularis horizontalis above, and below, tlie oval foramen nervi 

 acustici. A distinct crista cochlearis separates the vestibulum 

 from the semicanalis seu canalis lymphaticus which lies below 

 it, and which does not run horizontally as in the other lizards, 

 but obliquely downwanls and backwards from in front and 

 above. This forms the upper portion of the cochlea, the 

 outer and inner walls of which are constituted by tlie two 

 plates of cartilage, which fill up externally and internally the 

 gaps between the occipital and sphenoid bones, as we find is 

 similarly the case in tlie Chelonians. Of the foramen nervi 



