THE DEVELOPMENT OF THE SCALA TYMPANI, SCALA 



VESTIBULI AND PERIOTICULAR CISTERN IN 



THE HUMAN EMBRYO 



GEORGE L. STREETER 



Departmott of Enibri/ologij, Carnegie Institution of Washington, Johns Hopkins 

 Medical School, Baltimore, Maryland 



NINE FIGURES 



The study of the development of the large walled-off con- 

 nective tissue spaces that surround the membranous labyrinth 

 is particularly interesting in that it shows that they have a very 

 definite morphological individuality. It is evident at least 

 that they are not to be considered as insignificant accessories 

 that merely fill in the waste intervals between the membranous 

 labyrinth and the surrounding cartilage or bone. On the con- 

 trary, they have characteristics which are in many respects 

 as definite and constant as those of the ossicles themselves. The 

 individuality of these spaces in all respects is most marked. 

 They make their appearance at a definite stage in the develop- 

 ment of the embryo; they are formed at definite places; they 

 pass through a series of definite histogenetic processes; they 

 spread in a definite order and manner and eventually they at- 

 tain a definite form and structure. The general morphology 

 and relations of these spaces during their developmental period 

 will be described in the following paper, and the opportunity 

 will be taken to point out in the course of the description some 

 of these individualistic features. 



Instead of designating the large spaces surrounding the mem- 

 branous labyrinth as perilymphatic spaces, as has been the 

 general custom since the time of Breschet 1833, they will here 

 be spoken of as perioticular or periotic spaces. The use of the 

 term 'periotic' avoids the confusion arising from the incorporation 

 of the word lymphatic' in the terminology. The present ten- 



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