On the Perilymphatic Spaces of the Amphibian Ear. 227 



rities is caused by the flattening of the postero-ventral portion of the 

 space, over the area occupied by the fenestra vestibuli (fenestra ovalis). 

 There is here also another peculiarity, comparable with a feature first 

 described by Retzius (1. c.) in the Anura. In Triton the membrane of 

 the fenestra vestibuli is not attached all round to the margin of the 

 fenestra, but posteriorly is, as it were, pushed away from the margin 

 so as to form a small recess, the dorsal roof of which is part of the 

 floor of the capsule, whilst ventrally it is bounded by the membrane 

 containing the operculum (stapes). Within the recess is a perilym- 

 phatic space, opening anteriorly by a wide aperture into the spatium 

 sacculare (figs. 2, 3, 4, R.V.). The result is that in some trans- 

 verse sections, the operculum appears as a cartilaginous element lying 

 below the auditory capsule, and attached to it by membrane laterally 

 and medially (fig. 5, B. V.). The perilymphatic space however is clo- 

 sely applied to the inner face of the membrane over the whole of its 

 extent. The portion which passes out through the fenestra is compa- 

 ratively small. It may be described as the recessus fenestrae vesti- 

 huli. Eetzius gave the name of saccus fenestrae ovalis to a perilym- 

 phatic space having essentially similar relations in the Anura. Here 

 however the portion lying outside the capsule is in the anterior region 

 of the fenestra, and not in the posterior as in Triton. The two spaces 

 are closely comparable, inasmuch as they are both in all probability 

 the result of a tendency of the parts of the perilymphatic system to 

 grow out beyond the space in which they are confined, the outgrowths 

 occurring at the points of least resistance. 



The ductus perilymphaticus arises from the recessus just described. 

 It runs out laterally through an aperture in the bony shelf above the 

 recessus, passing first into the osseous canalis externus at its posterior 

 limit (fig. 2). The ductus bends first backwards then inwards below 

 the posterior end of the horizontal semicircular canal, and after mak- 

 ing a short loop passes over the posterior ampulla into the vertical 

 circle formed by the posterior canal and the posterior sinus of the 

 utricle. It here makes an irregular U-shaped bend, and then passes in- 

 wards and forwards anteriorly to the posterior sinus of the utricle, 



dorsally to the lagena and ventrally to the pars neglecta. The re- 



15* 



