124 



Irving Hardesty 



ments at the different turns were obtained from which to compute very 

 fair averages. Fortunately, one of the membranes from the pigs two 

 weeks old was more successfully manipulated, and, after mounting, was 

 so nearly intact and uninjured that a complete set of measurements 

 was obtained from it alone. The measurements of the membrane from 

 the foetuses at term averaged throughout so nearly identical with those 

 from the pigs of two weeks that one could infer no essential dimensional 

 differences between them. These transverse measurements were made 

 with an ocular micrometer whose spaces were standardized in terms of 

 microns. The measurements obtained from all the specimens gave the 

 following averages for the total width of the tectorial membrane in the 

 regions specified: 



tip of 

 basal 

 end 



58.1 



near I 7th ! 6th 

 basal j half- | half- 

 tip I turn j turn 



107.9 I 124.5 



5th 

 half- 

 turn 



4th 

 half- 

 turn 



3cl I 2d 1st 



half- ! half- half- 

 turn turn turn 



149.4 170.2 190.9 207.5 257.3 ' 307.1 



width tip of 

 near tip end at 

 at apex apex 



215.8 166.0 



The measurements of the tip at the apex were taken transversely 

 through the point at which the inner edge terminates, and those of the 

 basal tip, transversely through the point at which the outer edge ter- 

 minates (see Fig. 1). 



What is very apparent in the actual specimen may be perceived from 

 these figures, namely, that the tectorial membrane of the pig varies 

 widely in breadth, but varies gradually and somewhat progressively from 

 the basal end toward the apex. Each end terminates bluntly, the 

 widths of the tips taken at similar levels being much less than the 

 widths possessed l)y the half-turns to which they belong. The width 

 of the tip at the apex of the cochlea is nearly three times that of the 

 basal tip. At the apex the membrane rapidly increases to its greatest 

 width, which is attained in the first half-turn. From the basal end, it 

 increases in width gradually till the width in the first half-turn is 2.8 

 times greater than that of the last. 



Almost the entire variation of the tectorial membrane occurs in its 

 outer, free, portion, or that strip spreading from the outer edge of the 

 labium vestibulare (Huschke's auditory teeth) over the spiral sulcus 

 and the organ of Corti. That portion, or inner zone, which lies upon 

 and adherent to the labium vestibulare varies relativelv little in width. 



