On the Perilymphatic Spaces of the Amphibian Ear. 241 



towards the caviim perilymphaticum (fig. 26). The foramen perilym- 

 phaticum accessoiium has become part of the fissura metotica, and the 

 general arrangements are much as in the adult. In the latter how- 

 ever the spatium sacculare acquires a somewhat greater extent, inas- 

 much as it passes round the anterior border of the sacculus so as to 

 lie for a short distance on its inner as well as its outer side. In this 

 region it surrounds the branch of the auditory nerve which supplies 

 the macula of the sacculus. 



The conditions existing in the young stages of Bufo cinereus are 

 instructive. In a tadpole of 20 mm total length, the ductus perilym- 

 phaticus passes inwards and downwards from the upper part of the 

 spatium sacculare, giving off the recessus partis neglectae before rea- 

 ching the perilymphatic foramen. It can scarcely be said to pass into 

 the cranial cavity at this point, so that there is no spatium menin- 

 geal (figs. 30, 31). The foramen perilymphaticum inferius is at this stage 

 continuous with the foramen peril, superius, the combined aperture in 

 its anterior portion lying in the sagittal plane and in its posterior in 

 the horizontal (cf. figs. 30 and 33). Through the posterior part, which 

 represents the foramen perilymphaticum inferius, the recessus partis 

 basilaris leaves the cavum perilymphaticum (figs. 33—35). The com- 

 munication between the recessus and the ductus perilymphaticus is 

 direct, and in this respect resembles the condition in Urodeles, the duc- 

 tus reuniens being practically absent. The recessus partis basilaris 

 passes through the aperture into a portion of the cavum cranii which 

 lies in part below the inner border of the auditory capsule. The con- 

 ditions will be best understood from a study of figs. 29 — 35. We 

 cannot however call this the spatium meningeale, which always lies 

 further forward and is in direct continuity with the ductus perilym- 

 phaticus. It is in fact the saccus perilymphaticus, which reaches the 

 anterior end of the fissura metotica (fig. 35), by running first of all into 

 an apparent recess of the cranial cavity, as shown in figs. 33 — 35. 

 We have here then relations similar to those existing in an early 

 stage of Rana, and the question again arises as to whether the con- 

 tinuity of the two apertures and their relations to the cavum cranii 

 are more, or less, primitive than the condition found in the larval Pelo- 



Internationale Monatsschrift für Anat. u. Phys. XIX. 16 



