On the Perilymphatic Spaces of tlic Amphibian Ear. 237 



lias used the term foramen perilymphaticum superius, and the new 

 aperture in the base of the auditory capsule he calls the foramen 

 perilymphaticum inferius. Hasse spoke of the single aperture in the 

 Urodela as the "foramen rotundum", and the condition in the Anura 

 he regarded as equivalent to a "geteiltes foramen rotundum". Now 

 in the first place, the homology with the foramen rotundum has never 

 been established, and in the second, ray results lead me to the con- 

 clusion that the neiv aperture in the Anura has heen acquired inde- 

 pendently of the older one, although ontogenetically in some forms the 

 two apertures are the result of division of a single one. 



I shall therefore make use of the terms suggested by Gaupp, 

 which do not involve the acceptance of doubful homologies. 



We may now turn to the consideration of certain facts of ana- 

 tomy and development, which throw light upon the phylogeny and sig- 

 nificance of the perilymphatic spaces. 



In a larva of Felohates fuscus (total length 44 mm), we find 

 as usual a large spatium sacculare, extending upwards as far as the 

 sinus superior utriculi. The ductus perilymphaticus arises in its dorsal 

 and posterior region and runs at first backwards as a wide tube, along 

 the upper surface of the horizontal canal; it then curves round below 

 the posterior end of the canal and runs to the foramen perilymphati- 

 cum superius by a course similar to that already described in R. fusca. 

 The recessus partis neglectae is well developed, but the spatium me- 

 ningeale is as yet very restricted in extent (fig. 15). The large re- 

 cessus partis basilaris leaves the. auditory capsule by the foramen peri- 

 lymphaticum inferius, and expands to form the saccus perilymphaticus 

 (figs. 18 — 21). The latter is here a considerable sac, lying in a groove 

 in the floor of the skull, just below the partition between auditory cap- 

 sule and cavum cranii (fig. 21, S. P.). It has at this stage no rela- 

 tions to the fissura metotica, which does not extend so far forward as 

 the saccus. The connection between recessus partis basilaris and duc- 

 tus perilymphaticus does not, therefore, take place within the cavum cranii, 

 but by means of a canal — ductus reuniens — leading directly from the re- 

 cessus to the ductus perilymphaticus, and lying entirely within the 

 auditory capsule (figs. 18, 19, 20, D.B.). It runs along a groove in 



