PROPORTIONS OF THE TECTORIAL MEMBRANE 25 



The volumes of the different regions, computed in the above 

 way, represented by these areas, may be found to show the fol- 

 lowing proportional relations: (1) A given short length of the 

 apical end of the outspanning zone of the tectorial membrane 

 may be 41.7 times the volume of the same length of the basal 

 end of the zone. The volume of the same length of the 3rd half 

 turn may be 25.2 times, and that of the same length of the 5th 

 half turn may be 10.7 times the volume of that length of the 

 zone in the basal end. (2) Taken from the basal end toward 

 the apex, it may be found that between the basal end and the 

 region of the 5th half turn, the longest interval between measure- 

 ments, the volume of a given short length of the outspanning 

 zone may increase 90.7 per cent; between the 5th and the 3rd 

 half turns the volume of the same length may increase 57.4 

 per cent, and between the 3rd half turn and the apical end, 

 the volume of the same short length of the zone may increase 

 29.8 per cent. 



Just as does the width and thickness, so, as to be expected, 

 does the volume of the zone appear to increase progressively 

 from the apical toward the basal end. That the percentage of 

 increase toward the basal end of the cochlea is progressive rather 

 than regular must be due to the fact that, beginning with the 

 basal end, each turn of the coil is longer than the turn apical 

 to it and, therefore, there were greater lengths of the zone be- 

 tween the transverse lines at which the above measurements were 

 made in each succeeding coil from the apical toward the basal. 

 In studies made here of the teased out membranes of the adult 

 hog and in the studies of the membranes of pig fetuses at term, 

 published in the writer's previous paper, the tectorial membrane, 

 and therefore its outspanning zone, viewed as a whole appeared 

 to increase in width with uniform regularity from the basal into 

 the apical end. If the increase is irregular at all, the impression 

 may be obtained that it is less rapid in the basal than in the other 

 turns of the coil. Drawings illustrating the appearance of the 

 teased out membrane are given in the previous paper. 



The above variations in the proportions of the tectorial mem- 

 brane, assumed at least to approximate the normal adult, are 



