DEVELOPMENT OF THE SKULL OF EMYS 721 



The nervus acusticus exhibits a ramus vestibularis and a ramus 

 cochlearis. The former is the smaller of the two and is situated 

 sHghtly dorsal and somewhat anterior to the latter. They enter 

 the capsule through the foramina acustica anterius and posterius 

 respectively. The anterior foramen is situated at the extreme 

 anterior end of the pars cochlearis immediately ventral to the 

 recessus utriculi; the posterior foramen is situated nearer the 

 middle of the pars cochlearis, immediately in front of the postero- 

 medial lobe of the cochlear cavity and ventral to the cavum 

 utriculi. 



The nervus facialis finds its exit from the cranial cavity through 

 the foramen facialis which is situated a short distance dorsal to 

 the basal plate and in front of the anterior wall of the cochlea. 

 The ganglion facialis (s. geniculi) lies external to the chondrocra- 

 nium, separated from it by a thin layer of connective tissue, in 

 front of the foramen and dorsal to the lateral extension of the 

 basal plate already mentioned. The ganglion, accordingly, rests 

 in a broad groove between the basal plate on the ventral side and 

 the prefacial commissure, which unites the basal plate and otic 

 capsule, on the dorsal side. This groove is apparently the homo- 

 log of the fovea genicularis of the rabbit, as descritfed by Voit 

 ('08, p. 448). 



The ramus palatinus nervi facialis arises from the lateral aspect 

 of the ganglion facialis and passes in a ventro-medial direction 

 around the free edge of the crista substapedialis and then turns 

 in an anterior direction in the sulcus palatinus which is medial to 

 the rudimentary processus basipterygoideus on the ventral side 

 of the basal plate. 



The ramus hyomandibularis arises from the posterior end of 

 the ganglion geniculi and runs posteriorly in the fovea genicularis 

 and comes to lie further laterally and dorsally as it proceeds and 

 passes dorsal to the columella auris. At the level of the latter 

 the ramus hyomandibularis gives off the chorda tympani which 

 extends in a lateral direction along the dorsal margin of the colu- 

 mella and then turns sharply forward and ventrally to reach the 

 mandible, as Noack ('06) has already described. The- main 



