PROPORTIONS OF THE TECTORIAL MEMBRANE 



27 



scala tympani as layers of the membrane. The basilar mem- 

 brane proper and the layer of epithelioidal sjaieytiimi upon its 

 basal side vary very little in thickness in the different regions of 

 the coil and the little variation is irregular. 



POSSIBLE VIBRATION OF THE SPIRAL LAMINA 

 Varidtions of the spiral organ (of Corti) 



In the adult hog the spiral organ increases in both width and 

 thickness in passing from the basal toward the apical end of 

 the coil of the cochlea. Near the basal end (fig. 4) it may be 

 seen that the spiral organ proper is much thinner and narrower 

 than in the apical region (figs. 1-2). Reading the sections of 

 the organ consecutively in both sides of the median vertical 

 sections of the cochleae, or even reading figures 1 to 4, which 

 represent the organ in one side of a cochlea, it is suggested 

 that the increase in the size of the organ occurs uniformly from 

 base to apex. Measurements of the width and thickness of the 

 spiral organ as it appears in section in one side of five median 

 vertical sections gave the averages recorded in table 3. 



TABLE 3 



Giinng averages in micra of the widlh and thickness of the spiral organ, as measured 

 in one side of vertical median sections of cochleae of five adult hogs 



Width 

 Thickness 



1st half tcrn 



223.3 

 113.1 



3rd half turn 



221.1 

 104.4 



5th half turn 



208.7 

 85.2 



/TH HALF TURN 



130.0 



55.4 



The measurements of width of the spiral organ, averages of 

 which are given in table 3, were taken from the level of the 

 surface of the epithelium lining the internal spiral sulcus {ISS, 

 fig. 2) on the axial side of the organ to the level of the surface 

 of the cells of Claudius (CC, fig. 2). The measurements of 

 thickness of the organ were taken from the basilar membrane 

 proper through the middle of the outer hair cells to the vestib- 

 ular surface of the organ. As shown in figures 1 to 4, the vestib- 

 ular surface of the organ inclines axisward appreciably in the api- 



