226 H. S. Harrison, 



situated within the auditory capsule near the point where the duc- 

 tus passes through the foramen perilymphaticum. This space is in close 

 relation to the pars neglecta, and the endolymphatic and perilymphatic 

 cavities are here separated only by a very thin cellular membrane; 

 it may therefore be appropriately called the recessus partis negledae 

 (fig. 6, B.N.). Finally, there is, in some Urodeles at least, a short 

 diverticulum from the ductus, with similar relations to the pars basi- 

 laris; this space may be termed the recessus jtartis hasilaris (figs. 8, 

 9, 10, 13', B.B.). It attains much greater importance in the Anura 

 (figs. 14, 17, 25 etc.). 



In introducing these new terms, I do not wish to exaggerate the 

 degree of independence possessed by the parts they indicate. The 

 boundaries are somewhat arbitrary, and it is largely for the sake of 

 clearness and directness of description that I have found it necessary 

 to devise a special nomenclature. As will be seen, however, the terms 

 have a morphological as well as a practical, significance. 



We may now consider in some detail the perilymphatic system of 

 one of the Urodela, that namely of an adult Triton taeniatus. 



The description is taken chiefly from a wax-model of the audi- 

 tory labyrinth, with its nerves and perilymphatic spaces. 



The spatium sacculare is large (fig. 1, S.S.), and seen from the 

 side it completely hides from view the sacculus and lagena. It is 

 most extensive in the ventral and posterior region of the auditory 

 capsule. Seen from above its upper part lies within the circle formed 

 by the horizontal semicircular canal and the recessus utriculi, being in 

 contact with the recessus and the two ends of the canal. Its anterior 

 limit occurs immediately posterior to the bifurcation of the anterior 

 division of the auditory nerve, and its posterior limit is a little an- 

 terior to the ampulla of the posterior semicircular canal. It extends 

 dorsally as high as the lower part of the sinus superior of the utricle, 

 and venti'ally, to the floor of the capsule. Its outer surface is con- 

 vex, whilst the inner, which is in the main applied closely to the 

 outer convex wall of the sacculus (tympanal area), is concave. 



The space as a whole is therefore somewhat the shape of a con- 

 cavo-convex lens of rather irregular outline. One of the chief irregula- 



