306 GEORGE L. STREETER 



the periotic reticulum and the hiiueii of the scala. After reach- 

 ing this degree of development there is no evidence of any fur- 

 ther coalescence of the surrounding reticular spaces with the 

 main cavity. The membrane itself as seen in cross section con- 

 sists of rather compact nucleated strands of protoplasm, which 

 cannot as yet be separated into the so-called endothelial coat and 

 the supporting fibrous coat. However, a comparison of the 

 coagulated elements of the fluid seen in the reticular spaces 

 with those seen in the scala would indicate a difference between 

 the two and therefore it is probable that the membrane is 

 already partially impervious. 



Fig. 3 Detail of the section shown in figure 1, enlarged 400 diameters. It 

 shows the character of the margin of the scala vestibuli in a more mature con- 

 dition. The scala vestibuli is inclosed by a membrane consisting of the cells 

 that had previously constituted the reticulum occupying this area and which 

 have been modified in form in adaptation to the formation of this large tissue 

 space, closing it off from the surrounding tissue. 



DEVELOPMENT OF THE PERIOTIC CISTERN OF THE VESTIBULE 



Aside from the scala vestibuli and the scala tympani, the 

 largest of the periotic spaces is the large reservoir situated be- 

 tween the tympanic wall of the bony vestibuli with its articulated 

 stapes, and the vestibular chambers of the membraneous laby- 

 rinth. This is the spatium perilymphaticum vestibuli (BNA) 

 or the cysterna perilymphatica (Retzius). In order to eliminate 

 the word Iwiphatic from the terminology it will be designated 

 here as the Cisterna periotica vestibuli or less formally the peri- 



