PROPORTIONS f)F THE TECTORIAL MEMBRANE 59 



turn of the coil; (d) in volume, a given short length of the apical 

 end of the outspanning zone may be more than 41.7 times the 

 volume of the same length of the basal end of the zone. Be- 

 tween the basal end and the 5th half turn, the longest interval 

 between measurements in section, the volume of the outspanning 

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

 turns, the increase may be 57.4 per cent, and between the 3rd 

 and the 1st half turns, it may be 29.8 per cent. These variations 

 in the proportions are urged in support of the suggestion that 

 the tectorial membrane is far more adapted to serve as the 

 vibratory structure than is the basilar membrane. 



7. In the adult pig, the spiral organ (of Corti) increases appre- 

 ciably in both thickness and width in passing from the basal 

 to the apical end of the cochlea. 



8. That the membranous spiral lamina (basilar membrane) 

 may be thrown into vibration by certain strong stimuli is not de- 

 nied, and that the chief load carried by it, namely, the spiral organ, 

 increases in passing from the basal to the apical end of the 

 cochlea is considered as suggestive of its possible vibratory behav- 

 oir. The superior advantages of the tectorial membrane are 

 enumerated and some of its possible activities compared. 



9. Pig fetuses of a given length vary very much in the stages 

 of development of the cochlea, especially if from different litters. 

 For a given stage of development, it seems that fetuses obtained 

 in Louisiana average smaller than fetuses obtained in California. 



10. The cells of the lesser epithelial ridge, which differentiate 

 into the elements of the spiral organ, at an early stage produce 

 a delicate film of loosely arranged, imperfectly embedded fibrils. 

 These have been erroneously considered by some as increasing 

 to form an outer zone of the tectorial membrane; by others as 

 forming a permanent attachment of the membrane to the spiral 

 organ. It is urged that the cells of the lesser ridge, at first grad- 

 ing from the outer edge of the greater ridge, never actively en- 

 gage in the production of fibrils, and, as they differentiate into 

 the elements of the spiral organ, they cease the production alto- 

 gether. They contribute little, if anything, to the formation of 



