700 B. W. KUNKEL 



The basal plate is separated from the cupula posterior of the 

 otic capsule by the triangular, ventral portion of the fissiu^a 

 metotica; and from the cupula anterior by the fenestra prootica. 

 Between these two foramina the basal plate is continuous with 

 the capsule except for the foramen facialis which is so situated as 

 to leave a slender commissure uniting the basal plate and otic 

 capsule between itself and the fenestra prootica. 



The relations of the chorda dorsalis to the basal plate are of 

 considerable interest. In the embryo modelled the chorda passes 

 without interruption from the anterior face of the dens epistro- 

 phei into the posterior end of the condylus in which region it is 

 completely imbedded in cartilage. It is surrounded directly by 

 a sheath which is continuous with the perichondrium of the basal 

 plate in front and from which, in the region between the dens and 

 condylus, the ligamentum apicis dentis is derived. 



In front of the condj'le, where the basal plate becomes gradu- 

 ally thiimer, as far forward as the fenestra basicranialis posterior, 

 the chorda lies in the same plane with the basal plate and tends 

 to divide it into two symmetrical halves. The basal plate, accord- 

 ingly, is parachordal, as has been already described in the skull of 

 snakes, crocodilians, and Sphenodon; and not hj^^ochordal as in 

 Lacerta. This condition, however, is probably secondary, since 

 in younger individuals in which the condjde is not yet developed, 

 the basal plate immediately in front of the condylar region is 

 hypochordal to within a short distance of the fenestra basicraniahs 

 posterior where it becomes parachordal. 



The tissue immediately dorsal and ventral to the chorda in the 

 region posterior to the fenestra basicranialis posterior is reduced 

 to a very thin layer and is not fully chondrified in the stage mod- 

 elled. In passing through the fenestra basicranialis posterior the 

 chorda is enclosed in a membranous sheath which is continuous 

 with that which fills the fenestra, although it comes to lie in a 

 plane ventral to the basal plate. 



The chorda dorsalis is lodged posteriori}'' on the dorsal surface of 

 the crista sellaris in a deep groove whose sides gradually close 

 together anteriorly, converting the groove into a canal which 



