PROPORTIONS OF THE TECTORIAL MEMBRANE 21 



the first half turn is considered distorted and retracted axisward 

 by shrinkage (compare OZ, fig. 1, with fig. 2). In the table 

 as well as in the drawings, it appears less in width in this than in 

 the third half turn. This explanation of the shape of the sec- 

 tion of the apical end as due to shrinkage is supported by the 

 study of the tectorial membranes of fetal pigs described in my 

 previous paper. The depressed apical surface of the outer 

 edge of this zone as shown in figures 3 and 4 is also probably 

 the result of shrinkage. 



The attached axial zone (AZ, figs. 1 to 4) varies but slightly 

 in width in the different turns of the adult cochlea. In the 

 teased preparations, its width could be easily measured from 

 the fact that the line of imprint of Buschke's teeth {Ht, fig. 2) 

 upon the basal surface of the tectorial membrane could be seen. 

 In these, its width was found to conform quite closely to the 

 widths obtained by measurements from the sections (table 1). 

 In figures 1 to 4, the width of this zone appears practically uni- 

 form throughout and table 1 shows the maximum variation 

 to be but 16 micra, the zone being narrowest in the basal end 

 just as is the outspanning zone. It will be seen below that the 

 attached axial zone increases somewhat in general width between 

 the fetus and the adult hog. 



It must be remembered that the basal turn of the coil is much 

 the longest of the turns, has the greatest radius of curvature, 

 and that, therefore, there is a much greater distance or extent 

 of the membrane between the sections of the 7th and 5th half 

 turns than between the 5th and 3rd half turns, and especially 

 greater than between the sections measured of the 3rd and 1st 

 half turns, which latter involve the apical or shortest turn of 

 the coil. Thus, though the proportions of the tectorial mem- 

 brane may decrease uniformly from the apical to the basal end, 

 one must expect greater differences between the sections and 

 measurements which are taken transversely at the greater 

 distances apart. 



To sum up the studies made as to the width of the membrane, 

 with computations from table 1, it may be advanced (1) that 

 the membrane is widest at its apical end and decreases gradually 



