DEVELOPMENT OF THE SKULL OF EMYS 711 



dorsally it is separated from the prominences of the vertical 

 semicircular canals by a deep depression. The prominentia sac- 

 cularis is interrupted by the large fenestra vestibuli as well as by 

 the foramen glossopharyngei externum at its extreme upper 

 and posterior angle. The prominentia semicircularis posterior 

 rounds off the capsule postero-dorsally and rests ventrally on the 

 prominentia ampullaris posterior which is separated by a slight 

 depression from that of the semickcular canal. 



The median aspect of the capsule has a much more uniform 

 surface than the lateral one. The prominences of the two verti- 

 cal semicircular canals make a less conspicuous ridge framing 

 the capsule above than they do on the lateral side. Ventral to 

 the prominentia semicircularis anterior is the conspicuous depres- 

 sion, the fossa subarcuata, wliich separates it from the prom- 

 inentia recessus utriculi. Posterior to the ventral end of the 

 prominentia semicircularis anterior and ventral to the fossa 

 subarcuata is the inconspicuous triangular prominentia recessus 

 utricuh which is dorsal to the foramen faciahs and antero-dorsal 

 from the foramen acusticum anterius. Its posterior angle 

 extends dorsal to the foramen acusticum posterius and ventral 

 to the foramen endolymphaticum. Posterior to the foramen 

 endolymphaticum the prominentia sinus superioris utriculi 

 extends diagonally forward and upward and continues al its 

 upi^er end with the prominences of the two vertical semicircular 

 canals; posteriorly it merges imperceptibly into the prominentia 

 utricularis and ampullaris posterior. Ventral to the Une connect- 

 ing the dorsal margins of the two foramina acustica and glosso- 

 pharyngei internum is the semicircular prominentia saccularis 

 which bulges suddenly immediately behind the foramen facialis 

 and extends backward to the fissura metotica. 



The posterior wall of the cochlea is perforated near its median 

 margin by the fenestra cochleae, the anterior end of the canahs 

 perilymphaticus, as already described. The relation of these 

 parts is complicated in the stage modelled on account of the 

 extension posteriorly of the lateral wall of the cochlea so that the 

 canahs perilymphaticus opens posteriorly into a funnel-like 

 extension of the anterior end of the sulcus supracristularis. 



