Prof. A. M. Mayer's Researches in Acoustics, 447 



actions which must take place when a sound-wave traverses the 

 scalse. 



All know that the organ of Corti is enclosed in the ductus 

 cochlearis — a canal of triangular section bounded on two of its 

 sides by the scalae, and on its third by the membranes lining 

 the outer wall of the cochlea. The upper wall of this canal is 

 formed by the membrana Reissneri, which separates it from the 

 scala vestibuli ; and its lower wall is the lamina spiralis and the 

 elastic membrana basilaris which separate it from the scala tym- 

 pani. The ductus is closed at its upper end, and at its lower 

 end it communicates with the sacculus hemisphsericus by a fine 

 duct. The arch of Corti rests upon the membrana basilaris, 

 which extends beyond the base of the arch to the membra- 

 nous outer wall of the cochlea ; and over the arch spreads the 

 membrana tectoria, covering the rods of Corti and the hair- 

 cell cords as with a roof, but leaving the outer portion of the 

 elastic membrana basilaris exposed. We will now show that 

 the significance of these anatomical relations is to bring the 

 sound-vibrations to act with the greatest advantage on the co- 

 vibrating parts of the ear, and to cause these parts to make one 

 half as many vibrations in a given time as the tympanic or 

 basilar membranes. 



The relations which the form of the scalse bears to the sono- 

 rous waves traversing them, will be modified according to the 

 existence or non-existence of a communication between the scala?. 

 On this point there seems to be some difference of opinion*; 

 and therefore I will attempt to explain the functions of the 

 scalse first on the supposition that they are continuous, and 

 then on the assumption that they are not continuous, but closed 

 at the place where the helicotrema is supposed by most anato- 

 mists to exist. 



E. Weber was the first to point out the peculiar molecular 

 actions which exist when the dimensions of a body are very small 

 compared with the length of the sonorous waves which traverse 

 it ; and Helmholtz based his investigations on the Mechanism 

 of the Ossicles of the Ear on the theory of Weber, which 

 Helmholtz gives in these words : — u The difference in displace- 

 ment of two oscillating particles whose distance from one an* 

 other is infinitely small compared with the wave-length, is itself 



* Dr. Albert H. Buck, of New York, writes me :— " that in 1870 1 under- 

 took to demonstrate the existence of the helicotrema by making sections 

 through the cochleae of an infant at right angles to the base. In this I 

 utterly failed; and although able to obtain a good view of the last part of 

 the dividing septum, both from below and from above, neither Professor 

 Helmholtz nor I could detect the slightest trace of an opening. Of course it 

 would not do to base my denial of the existence of the helicotrema upon 

 the results of but a single investigation." 



