248 Mr. R. Moon on the Functions of the Membranous 



the fall, and is broken transversely as it crosses the brow. It de- 

 scends the fall as a succession of broken cliffy ridges with trans- 

 verse hollows between them. In these latter the ice-debris and 

 dirt collect, partially choking up the fissures formed in the first 

 instance. Carrying the eye downwards along the fall, we see, as 

 we approach the base, these sharp ridges toned down, and a little 

 below the base they dwindle into rounded protuberances which 

 sweep in curves across the glacier. At the centre of the fall 

 there is not a trace of the true [veined] structure to be observed. 

 At the base of the fall it begins to appear — at first feebly, but 

 soon becomes more pronounced, until finally, at a short distance 

 below the fall, the eye can follow the structural grooving right 

 across the surface of the glacier, while the mass underneath 

 has become correspondingly laminated in the most beautiful 

 manner"*. 



XXXIII. On the Structure of the Human Ear, and on the Mode 

 in which it administers to the Perception of Sound. By R. Moon, 

 M.A., Honorary Fellow of Queen's College, Cambridge. 

 [Continued from vol. xxxviii. p. 376.] 

 On the Functions of the Membranous Labyrinth and of the Semi- 

 circular Canals. 

 IN my previous papers I have proceeded on the assumption 

 that, in those animals whose auditory apparatus includes a 

 cochlea, the perception of aerially conveyed sounds is occasioned 

 by the alternate ebb and flow of the liquor Cotunnii from the 

 cochlear aperture, along the scalse, to the vestibular aperture, and 

 vice versa; and my efforts have been mainly directed to pointing 

 out the mode in which this alternate motion of the aural liquid 

 is mechanically effected. 



It is clear that this motion can in no degree be dependent 

 upon the action, or even upon the existence, of the membranous 

 labyrinth or of the semicircular canals. Whether it is capable of 

 affecting the nerves expanded within the former is a different 

 question, and one which will require consideration; but up to 

 this point I have made no attempt towards explaining the func- 

 tions, or accounting for the strange form exhibited by the mem- 

 branous labyrinth. To this part of the subject I now propose 

 to address myself. 



Upwards of forty years have elapsed since the late M. Flourens 

 demonstrated in the most conclusive manner, by means of expe- 

 riments performed upon living subjects, that the semicircular 

 canals in birds and in mammalia have functions totally uncon- 

 nected with the sense of hearing. 



* Phil. Trans. 1859, part i. p. 284. 



