DEVELOPMENT OF THE SKULL OF EMYS 709 



instead of anteriorly so that the unique condition is met with in 

 that the nervus glossopharyngeus passes through the cavity of 

 the cochlea in its passage from the cranium to the exterior, as 

 will be described more fully later. On its lateral aspect the prom- 

 inentia saccularis is semicircular with its convexity below. It 

 is situated behind the foramen facialis and the prominentia 

 recessus utriculi and beneath the prominentia semicircularis 

 lateraUs, and passes posteriorly beyond the foramen glosso- 

 pharyngei externum. Its ventral wall is the basal plate. As 

 already mentioned the prominentia saccularis is apparent from 

 the ventral side of the skull as a gentle convexity of the basal 

 plate which lies behind the level of the fenestra basicraniahs pos- 

 terior. On the median aspect of the otic capsule the prominence 

 extends posteriorly from the region of the foramen acusticum 

 anterius posteriorly as far as the anterior angle of the fissura 

 metotica. The convexity of the prominentia saccularis medially 

 is more pronounced in its anterior portion immediately behind 

 the slender side piece through which the n. facialis passes than 

 posteriorly so that the foramen acusticum anterius, which is 

 situated in this region, comes to face somewhat anteriorly as 

 well as medially. 



The crista parotica forms a stout prismatic structure with its 

 ventral surface horizontal and extending forward from the ven- 

 tral limits of the prominentia ampullaris posterior and projecting 

 freely for a very short distance in front. 



The fenestra vestibuU (s. ovalis) (f.v., fig. 28) is situated in the 

 ventral part of the lateral wall of the otic capsule, in the middle 

 of the saccular region between the foramen glossopharyngei 

 externum and foramen facialis, slightly nearer the former than 

 the latter. It is of equilateral triangular form to accommodate the 

 foot plate of the columella auris. Its ventral margin is hori- 

 zontal and is formed by the basal plate which projects laterally 

 beyond the capsule as a kind of horizontal shelf on which the foot 

 plate of the columella rests (fig. 5) . 



Behind the fenestra vestibuli and separated from it by a 

 slender rod sloping obhquely postero-ventrally, is the external 

 opening for the n. glossopharyngeus (f.g.e., fig. 28). This is 



JOURNAL OF MORPHOLOGT, VOL. 23, NO. 4 



