28 \\\T«>Mi« \i \M. PHYSIOLOGICAL STUDIES ON 



Hensen's supporting cells are also fully developed. Through 

 the development of Deiters' and Hensen's cells a change is 

 effected in the course of the lamina reticularis. It runs no longer 

 parallel to the plane of the nieinbrana basilaris, but dips inward. 



Though the membrana basilaris remains nearly stationary in 

 it- breadth, the thiekness of the tympanic covering layer is 

 reduced and the Longitudinal nuclei in the zona pectinata diminish 

 in number. 



The membrana tectoria reaches in the basal turn to the outer- 

 most row of the outer hair cells, but the apical turn only to the 

 second row. The so-called 'outer marginal zone' connects with 

 the terminal frame ( Schlussrahmen) of the lamina reticularis. 



In the next stage, the twenty-day-old rat (tig. 10), the papilla 

 spiralis ami the tissues about it are developed almost com- 

 pletely; therefore, the structural relations of the cochlea accord 

 nearly with those of the adult cochlea, as generally recognized 

 in histology. 



It is to be rioted here that in the basal turn, Bottcher's cells 

 are to be seen in sulcus spiralis externus as a cell group situated 

 on the outer part of the vestibular surface of the membrana 

 basilaris. This cell group consists of several granular compact 

 and sharply bounded cells entirely covered by high swollen cells 

 • in all sides. That this cell group belongs to the epithelium of 

 the sulcus -piralis externus can be easily demonstrated. While 

 the cells in this group show no particular changes in structure, 

 the neighboring cells diminish in their height and size towards 

 the apex, and finally become similar to the former. After twenty 

 days of age the general features of the cochlea are those of the 

 adull and do not require general description. The finer differ- 

 ences will be discussed in subsequent chapters. 



Figure II shows the relations at 100 days and figure 12 at 

 5 16 days. 



Membrana tectoria. As stated above, this membrane is 



divided into two /.one-, aii outer and inner, using the outer edge 



"t" the labium vestibulare as the point of division (fig. 1, 7-7'). 



h zone was again divided into two equal parts at 6-6'and8-8'. 



Thus the sum of the breadths of the two outer parts represents 



