On the Perilymphatic Spaces of the Ampliibiaii Ear. 223 



tissue are intermingled. Arising from this general perilymphatic space 

 he found in the frog and other Anura two canals, the ductus peri- 

 lymphaticus and the ductus fenestrae ovalis. The former of these was 

 discovered by Hasse, who called attention to its close association with 

 the labyrinth at certain points; it has been observed by several sub- 

 sequent workers. Owing to failure in recognising that the ductus peri- 

 lyraphaticus opens, not into an extensive space surrounding the whole 

 labyrinth, but into a restricted space lying in the region between the 

 outer lateral wall of the sacculus and the membrane of the fenestra 

 vestibuli (ovalis), the complete physiological significance of the peri- 

 lymphatic system has never been realized. I hope to prove in the 

 present paper that the disposition of tissues and fluids within the 

 cavum perilymphaticum is such as to allow of the transmission of 

 vibrations from the membrane of the fenestra vestibuli, through the 

 perilymph, to certain parts of the wall of the membranous labyrinth, 

 and to these parts alone. The labyrinth is not surrounded by fluid;, 

 on the contrary the enclosing space is occupied jpartly hy connec- 

 tive tissue, and partly hy definite, constant, and restricted spaces, 

 containing a non-corpuscidar fluid, the perilymph. It is therefore 

 necessary to distinguish between perilymphatic tissue, in which fixed, 

 formed elements predominate^), and perilymphatic spaces, which are 

 bounded by well-defined walls and have fluid contents only. It is only 

 over certain areas, three in number, of the pars inferior of the laby- 

 rinth, that vibrations of the perilymph are in a position to affect the 

 endolymph in a definite manner. Over these areas the labyrinth wall 

 remains thin, the cells indeed becoming flattened ; over the rest of the 

 wall thickening takes place by the development of a dense, almost carti- 

 laginous layer ("Spindelknorpel" of Retzius), consisting of specialized 

 perilymphatic tissue. To the thin areas the perilymphatic spaces are 

 applied, so that the dividing wall between perilymph and endolymph con- 

 sists of two layers, the ectodermal epithelium of the labyrinth and the 

 pavement endothehum of the perilymphatic space. These thin mem- 

 branes, being attached all round their periphery to thicker parts of the 



^) The amount of fluid within the interstitial spaces of this tissue varies in 

 different regions, being apparently greatest around the canals. 



