DEVELOPMENT OF PERIOTIC TISSUE SPACES 



309 



latter there is a definite row of reticular spaces actively coalescing 

 and constituting the beginning of the scala vestibuli. The 

 scala tympani is already well started at this time, but its de- 

 velopment is quite independent of the cistern. Within the 



SACCUS ENDOL. 



DUCTUS 

 j" g COCH. 



Fig. 4 The figiu'es 4 to 9 represent a series of median and lateral views of 

 wax-plate reconstructions of the membranous labyrinth and the surrounding 

 perioticular tissue spaces, illustrating under the same scale of enlargement 

 three typical stag]es in the development of these spaces. This figlire shows a 

 lateral view of a model reconstructed from a human fetus 50 mm. CR length 

 (Carnegie Collection, No. 84). The scala vestibuli is in the first stage of its 

 development and consists of a row of large reticular spaces which extend from the 

 ventral margin of the cistern do'wnward along the apical surface of the cochlear 

 duct. The scala tympani is more advanced and sho\vs more complete coales- 

 cence of its constituent spaces. Enlarged 9 diameters. 



Fig. 5 Median view of the same model shown in figure 4. This view shows 

 the topography of the scala tympani. Its large proximal end lies opposite the 

 fenestra cochleae and corresponds to the focus at which its development origi- 

 nates. Distally it tapers off rapidly, where the spaces are smaller and their 

 coalescence less complete. Enlarged 9 diameters. 



cistern can be seen scattered clumps of faintly refractive granular 

 threads of what seems to be a coagulated constituent of the 

 plasma. 



The subsequent growth of the cistern is shown in figures 6 

 to 9. Figures 6 and 7 show respectively a median and lateral 

 view of a wax-plate reconstruction of the membranous labyrinth 

 and its perioticular spaces in a human fetus 85 mm. long (Car- 



