28 ANATOMICAL AND 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 membrana basilaris, but dips inward. 



Though the membrana basilaris remains nearly stationary in 

 its breadth, the thickness 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 (fig. 10), the papilla 

 spiralis and 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 noted 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 

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

 the sulcus spiralis 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 

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

 ences will be discussed in subsequent chapters. 



Figure 11 shows the relations at 100 days and figure 12 at 

 546 days. 



1. Membrana tectoria. As stated above, this membrane is 

 divided into two zones, an outer and inner, using the outer edge 

 of the labium vestibulare as the point of division (fig. 1, 7-7'). 

 Each 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 



