ACTION OF THE TECTORIAL MEMBRANE 477 



and from the same variety of cells as the spiral organ (both being 

 of ectodermal origin). The so-called basilar membrane is not 

 always coextensive with the spiral organ. 



(2) In position, the tectorial membrane lies over the apical 

 or vestibular surface of the spiral organ and thus may be first 

 and more directly acted upon by the usual sound vibrations, since 

 these are imparted by the basis of the stapes directly to the fluid 

 in the scala vestibuli. The basilar membrane lies under the 

 basal side of the spiral organ and next the scala tympani, the 

 thick spiral organ, the tectorial membrane and the vestibular 

 membrane intervening between it and the scala vestibuli. 



(3) In the other sense organs, and all sensitive surfaces, the 

 impulses are aroused at the peripheral or outer surface of the 

 epithelium. The tectorial membrane lies over the peripheral 

 surface of the spiral organ while the basilar membrane lies under 

 the organ. The membranes of the maculae and cristae, whose 

 origin is directly homologous with that of the tectorial membrane, 

 arouse impulses at the peripheral surface of their respective neuro- 

 epithelia. 



(4) When the two are teased out for examination in the fresh, 

 the tectorial membrane is found to be far more flexible than the 

 basilar membrane. 



(5) The tectorial membrane is considered more adapted for 

 application of the telephone theory, capable of being more freely 

 agitated, in that one edge of its supposedly vibratory portion, 

 its outspanning zone, is free, while the basilar membrane is 

 merely a flat tendon, one edge continuous from the tympanic 

 lip of the spiral lamina and the other continuous into the spiral 

 ligament. Furthermore, not only are both edges of the basilar 

 membrane attached or continuous with the wall of the labyrinth, 

 but it is loaded on its two sides by thick layers of other tissues 

 likewise continuous beyond its edges and thus it must be less 

 readily agitated than is the tectorial membrane, certainly by the 

 vibrations of lesser amplitude. 



(6) Figure 1 is given to show the shape of the tectorial mem- 

 brane of the adult hog viewed on the flat from the basal surface, 

 its coil slightly opened to obviate the overlapping in its natural 



