248 H. s. Harrison, 



through the aperture except the perilymphatic space. As I have 

 pointed out, the conditions are loest shown in the larva of Felohates 

 fusais (figs. 17 — 21). It is significant that in the development of the 

 parts in Rana fusca, the first portion of the perilymphatic system to 

 appear is the recessus partis basilaris, although this is clearly the most 

 recently acquired space. It appears in ontogeny sometime before the 

 older portions and is at first so situated as to suggest that its actual 

 presence prevents the formation of cartilage over the area that remains 

 unchondrified as the foramen perilymphaticum inferius. Everything in 

 fact points irresistibly to the conclusion that the recessus partis basi- 

 laris has been the direct cause of the formation of the foramen peri- 

 lymphaticum inferius of the Anura. On the other hand the evidence 

 for my view as to the origin of the foramen perilymphaticum (superius) 

 and the fenestra vestibuli is less direct. At the present day the fora- 

 mina exist before the spaces are developed. This may however be ex- 

 plained by the not improbable assumption that the apertures are old 

 acquirements even in the Urodela and are now developed independently 

 of the perilymphatic spaces which were the original causes of their 

 formation. 



Attention must be called to certain other points with regard to 

 the relations between the spaces and the foramina. The foramen peri- 

 lymphaticum (superius) is not bounded by a membrane, the ductus 

 perilymphaticus passing through it to become the spatium meningeale. 

 On the other hand, the foramen perilymphaticum inferius and the fe- 

 nestra vestibuli both have membranes more or less coextensive with 

 them in extent. In the case of the former the membrane is continous 

 lüith the perichondrium of the outer surface of the chondrocranium. 

 The same is true of the membrane of the fenestra vestibuli (fig. 36), 

 although here the continuity is less obvious and is more liable to be 

 overlooked. Gaupp [7] says, in speaking of the primary fenestra vesti- 

 buli of Rana fusca at 14 mm: "Geschlossen ist es zur Zeit durch einen 

 kernreichen Gewebszug, der als unmittelbare Fortsetzung des Basal- 

 plattenknorpels erscheint und aussen in den Knorpel am äusseren 

 Bogengänge übergeht. Nur in den mittleren Partien, wo sich später 

 das "secundäre Foramen ovale" erhält, ist das Gewebe nicht in den 



