DEVELOPMENT OF PERIOTIC TISSUE SPACES 303 



ment of its constitiiont cells. In its final form the margin of the 

 space roughly resembles an endothelial membrane. Immediately 

 lining the space is a thin membrane with flattened nuclei which 

 is supported underneath by a thin coat of nucleated protoplasm 

 that has the form of fibrous connective tissue. The former, 

 judging only from its final appearance, could be designated as 

 endothelium, thus making a distinction between it and the 

 underlying tissue. In its histogenesis, however, it differs in 

 no way from the rest of the wall and the difference that exists 

 later seems to be merely the result of its adaptation to the exist- 

 ing physical conditions. Its early behavior is entirely different 

 from that of vascular endothelium. Therefore if one uses the 

 term endothelium for its designation this must be done with a 

 considerable amount of reservation. 



These phenomena can be particularly well studied in the 

 scalae while they are in the process of spreading and enlarging. 

 As we shall see, the scalae are more mature in their proximal 

 portions and are progressively less mature as one approaches 

 the apex of the cochlea. Thus any one specimen shows several 

 stages in the development. Typical views showing some of 

 the steps in this process are represented in figures 1 to 3. Figure 

 1 represents a section through the second turn of the cochlea in 

 a human fetus 130 mm. CR length (Carnegie Collection, No. 1018). 

 It shows the topography of the cochlear duct and the general 

 character of the perioticular spaces that are developing along 

 its inner margins. The upper one or scala vestibuli is in a more 

 mature condition. The lower one or scala tympani is less ma- 

 ture and along its peripheral (right) margin, it is in the act of 

 spreading so as to underlie, as it eventually will do, the future 

 basilar membrane. The scala tympani finally reaches the periph- 

 eral margin of the cochlear duct, and it does this by the coales- 

 cence of the enlarging reticular spaces which become incorporated 

 with the main cavity of the scala. 



This area is a particularly good one for studying the histo- 

 genesis of these spaces. It is shown under higher magnification 

 in figure 2, which is a detail of the same section. By comparing 

 this figure with figure 1, the exact location can be readily made 



