410 



Mr. H. J. Watt. 



perhaps as contrasted with quasi-pendular movement, exhibits an efficiency 

 oarying directly with the weight or mass in such a way that the cost is 

 diminished by increase of mass, as if the different mechanical considerations 

 involved in this separable process arranged the mass in the other pan of 

 the scales of cost. 



The Typical Form of the Cochlea and its Variations. 

 By Henry J. Watt. 



(Communicated by Prof. D. Noel Paton, F.Pv.S. Received October 3, 1916.) 



The work of this paper is based upon the photographic and descriptive 

 material presented by Dr. A. A. Gray in his two volumes on ' The 

 Labyrinth of Animals,' published by J. and A. Churchill, London, in 1907 

 and 1908.* I have succeeded in extracting from that impressive mass of 

 material definite results that seem to be of some importance. 



The dimensions of the cochlea measured by Dr. Gray are : (1) the 

 diameter of the lowest whorl and (2) of the second whorl (" taken in a 

 plane which passes vertically through the apex of the cochlea and the 

 anterior margin of the round window") ; (3) the diameter of the tube of the 

 cochlea in front of the round window; (4) the major axis of the oval 

 window : (5) the slant height of the cochlea (" the distance from the upper 

 margin of the round window to the apex of the organ ") ; and (6) the number 

 of turns of the cochlea. 



I found it desirable to add to these a measurement of the total length of 

 the basilar membrane. That must surely represent more closely and 

 directly than anything else the pitch-range of hearing. Fortunately, a 

 close study of Gray's wonderful photographs showed that an approximate 

 measurement of the length of the basilar membrane (as of the outside edge 

 of the cochlear tube) could be got from them. The symmetrical shape of 

 the cochlea makes it possible to measure the diameters of the successive 

 whorls, no matter from what angle the photograph was taken. (The reader 

 must consult Gray's pictures.) With the help of Gray's measurements of 

 the diameters of the first and second whorls, by close attention to the 

 consistency of these with the dimensions visible in the photograph, and by a 

 careful comparison of the different photographs showing the cochleas of 



* Cf. also 'Koy. Soc. Proc., : B, vol. 78, p. 284 ff. (1906), and B, vol. 80, p. 507 ff. (1908). 



