DEVELOPMENT OF PERIOTIC TISSUE SPACES 317 



PERIOTIC SPACES OF THE SEMICIRCULAR CANALS 



From the descriptions given of the adult the reticulum along 

 the canals never develops a single continuous wide periotic space 

 like that of the cistern and the two scalae. There always re- 

 main a few trabeculae such as are seen in the cistern and sca- 

 lae in their earlier stages, and these constitute partitions which 

 subdi^'ide the space and give it the appearance of a series of 

 separate spaces extending along the inner margms of the canals. 

 Although these spaces along the canals are incomplete as com- 

 pared with the cistern and scalae, they are however entirely 

 analogous with them in their formation. 



The space along the lateral canal is the largest. Its posterior 

 end exists as a continuation of the cistern. This can be seen in 

 the lateral view of the model shown in figure 8 where the cistern 

 extends for a considerable distance along the inner border of 

 the lateral canal. Along the other two canals of the same speci- 

 men (130 mm., CR length) the reticulum has commenced the 

 process of space-formation, but complete channels are not yet 

 established. 



COMMUNICATION OF THE PERIOTICULAR SPACES WITH THE 

 ARACHANOID SPACES 



The relation of the scala tympani and scala ^'estibuli to the 

 subarachnoid spaces surrounding the hind-brain is of consider- 

 able interest both on account of the possibility of their functional 

 relationship and on account of the similarity that exists in their 

 development. For a satisfactory investigation of the establish- 

 ment and the character of the communications that are formed 

 between these two allied systems of tissue-spaces one should re- 

 sort to other methods than those used in the present study, and 

 furthermore one should examine older fetuses than those de- 

 scribed here. Certain observations, however, were made in the 

 course of the abo^'e investigation that bear a relation to these 

 matters, and they will be briefl}^ outlined here. In the first 

 place the histological picture of the periotic reticulum is essen- 

 tially the same as the early stages of the pia-arachnoidal tissue, 



