DEVELOPMENT OF PERIOTIC TISSUE SPACES 313 



in the form of the reticular cells which repeatedly adapt them- 

 selves to the new conditions. There is no evidence to indicate 

 that any other cells take part in the formation of the scalae. 



The first evidence of the formation of scalae is found in fetuses 

 about 40 nun. long, which is a little later than the first appear- 

 ance of the cistern. In a fetus 43 mm. CR length (Carnegie 

 Collection, No. 886) along the proximal part of the cochlear 

 duct on its basal surface, there is a distinct widening of the meshes 

 of the periotic reticulum. This is the beginning of the scala 

 tympani. On the opposite side of the cochlear duct where 

 one would look for the scala vestibuli the periotic reticulum 

 retains its primiti^'e appearance characterized by a narrow and 

 rather uniform mesh. Thus the scala tympani makes its ap- 

 pearance slightly in advance of the scala vestibuli, that is, if we 

 regard the latter as distinct from the cistern. 



In fetuses 50 nnn. long both the scala tympani and the scala 

 vestibuli can be plainly identified, although they are still very 

 incomplete. A wax-plate reco'nstruction of them representing 

 their form and their relation to the membranous labyrinth in a 

 human fetus 50 mm. CR length (Carnegie Collection, No. 84) 

 is shown in figures 4 and 5, being a median and a lateral view 

 respectively. It will be seen that the scala tympani is larger 

 and more advanced in its development than the scala vestibuli. 

 The latter is in its earliest stage and consists of hardly more than 

 a row of enlarged reticular spaces that extend downward from 

 the cistern along the dorsal and apical surface of the cochlear 

 duct. 



The scala tympani consists of an elongated oval space lying 

 along the basal surface of the proximal part of the cochlear 

 duct, about corresponding to the proximal half of the first turn 

 of the duct. In the main part it is a single space with a distinct 

 margin separating it from the general periotic reticulum. In 

 the more apical portion it tapers off into multiple incompletely 

 united smaller spaces which actively coalesce as the process 

 advances into the new territory along the duct. It is of interest 

 to note that the most mature and the largest part of this scala^ 

 representing the focus at which it first appeared, is opposite 



