384 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



Whether the sac, receptaculum dorsale (rsi), acts as a reservoir .for 

 this fluid or serves to receive any excess driven out of the atria, I am 

 unable to say, but its distension is not likely to produce any imme- 

 diate effect on the spinal cord, separated as it is from it by the thick 

 cushion of loose adipose tissue which would entirely redistribute any 

 pressure. That the forward movement of the fluid in the cavum 

 sinus imparts should have any direct effect on the base of brain, as 

 suggested also by Hasse, is, I conceive, improbable, owing to the 

 thick cushion of adipose tissue which separates the brain from the 

 floor of the skull. (Fig- 9, PL VI.) I am inclined to believe, 

 then, that it is solely through the auditory nerve, and specially through 

 its saccular branches, that the central nervous system is informed of 

 the movements of malleus and stapes, and consequently of the state 

 of distension of the air-bladder. 



It is probable that the currents in the endolymph produced in this 

 way are different in character from those brought about by ordinary 

 sound waves, but on the other hand the difference is not likely to be 

 of such moment as to remove the phenomena in question entirely 

 from the domain of sound. 



Whether the air-bladder and apparatus in connection with it are 

 also sensitive to the alternations of pressure incident to sound waves, 

 and whether this be not one of the principal channels through which 

 the endolymph of the partes infer tores of the labyrinth is set in 

 motion, must be a matter for further investigation. No very free 

 interchange of endolymph can take place between the superior and 

 inferior parts of the labyrinth, for the ductus sacculo-utricularis is 

 thick walled and its narrow lumen is blocked up by a valve project- 

 ing obliquely across it. Although the endolymph, then, in the 

 superior part may be very readily set in motion by the vibrations 

 transmitted through the thin wall of the skull opposite the recessus 

 utriculi, yet the inferior part must be in a great measure protected 

 from such by its concealed position. 



Hasse (I.e. 599) while not entirely excluding the possibility of 

 alterations in volume of the air-bladder exerting an influence on the 

 production of auditory sensation, adduces several arguments for 

 believing that such must be of very subordinate nature in the 

 Cyprinida. The first of these is that the direction of the stroke 

 of the stapes not being coincident with the plane of the apertura 

 posterior of the cavum, the fluid contents of the atrium will not be 



