CHONDROCRANIUM OF EUMECES 143 
posteriorly, slender and tube-like to the anterior, where it passes 
dorsal to the endolymph duct and extends forward into the cavum 
vestibulare anterius. Here it expands again to form the recessus 
utriculi. The posterior enlargement of the utriculus connects 
with the anterior and posterior semicircular canals by way of the 
sinus superior, lying in the recessus of the same name, and sepa- 
rately with the posterior limb of the lateral canal; it has also a 
connection with the posterior ampulla, which occupies the re- 
cessus ampullaris posterior. While the form of the cavum vestib- 
ulare posterius gives little suggestion of its complex contents, 
the cavum vestibulare anterius is far more expressive. As seen 
in lateral view, it is rather definitely triangular and noticeably 
inflated in the neighborhood of each angle. The posteroventral 
angle contains the recessus utriculi, already mentioned, while the 
anterior and lateral ampullae lie in the anterior and postero- 
dorsal angles, respectively. 
In the cast (fig. 5) the fenestra vestibuli (fen.vest.), fenestra 
cochleae (fen.coch.), and anterior acusticus foramen (f.n.VIIJ.a.) 
are represented by projecting plugs, and the impressions of 
neighboring cartilages appear as hollows in the plugs—the foot- 
plate of the columella auris in that of the fenestra vestibuli and 
the edge of the basal plate in that of the fenestra cochleae. The 
foramen endolymphaticum and the posterior acusticus foramen, 
on the median side of the cavum vestibulare posterius and of the 
transition from this cavum to the cavum cochleare, respectively, 
are not seen in the figure. 
The thin plates of cartilage separating the semicircular canals 
from the cava vestibularia, anterius and posterius, are named 
by Gaupp the septa semicircularia—anterius, laterale, and post- 
terius respectively. The transverse plate between the two cava 
vestibularia is known as the septum intervestibulare; the fora- 
men through which the two cava communicate is the foramen 
intervestibulare. In the turtles, Emys (Kunkel, 712 b), Der- 
mochelys, Chelone, and Chelydra (Nick, ’12), the septum inter- 
vestibulare is wanting, and the anterior and posterior chambers 
unite in a common cavum vestibulare; in Chelydra Nick also 
