On the Perilymphatic Spaces of the Amphibian Ear. 233 



by the forward growth of the posterior border of the fenestra, which 

 takes place so as to form the roof above the recessus. It is worthy 

 of note that the roof is not preformed in cartilage, this and other facts 

 suggesting that the restriction of the fenestra vestibuli is a secondary 

 process (figs. 4, 5). 



Ossification extends forwards slightly beyond the origin of the 

 ductus, and leaves a small aperture through which this canal leaves the 

 recessus (figs. 2, 3). 



III. The Perilymphatic System in the Anura. 



The perilymphatic system of the Anura can be traced with great 

 clearness to a further development of the corresponding parts in the 

 Urodela. The chief advance is associated ivith an increase in the 

 size and importance of the recessus partis hasilaris, and an alteration 

 in its position. This change is concomitant with the progressive de- 

 velopment of the pars basilaris, which becomes of much greater 

 functional importance in the group now under consideration. From a 

 position immediately dorsal to the lagena in the Urodela, it comes in 

 the Anura to lie mainly posterior to this structure, attaining also a 

 much greater degree of independence. It is situated nearer to the 

 floor of the capsule, and since the perilymphatic recessus is chiefly 

 ventral to the pars basilaris, the former is brought into direct contact 

 with the cartilage of this region, with results to be presently indi- 

 cated. Another effect of the change in position of the two associated 

 structures, is seen in the fact that in some forms the recessus is no 

 longer in immediate communication with the ductus perilymphaticus as 

 it is in Urodeles, but is drawn out into a short canal, which for de- 

 scriptive purposes we may call the ductus reuniens (see Diagrams 

 2 and 3). 



Hasse [1] arrived at a very different conclusion as to the course 

 taken by the modifications, inasmuch as he apparently considered that 

 the recessus partis basilaris is a portion of the ductus lying in the 

 direct course from the spatium sacculare to the spatium meningeale. 

 Retzius appears to be of the same opinion. Villy's results are vitiated 

 by his mistake of describing the pars basilaris as the lagena; in ad- 



