ox THE AXATOMT OF FISHES. 
267 
actual or molecular, imparted to the fluid contained in those cavities must be trans- 
mitted to the endolymph of the sinus and ductus endolymphaticus, and eventually to 
that which fills the two sacculi, and finally act as a stimulus to the sensory epithelium 
of the latter. Ramsay Wright has briefly discussed the influence exerted by the 
movements of the scaphia on the fluids of the membranous labyrinth, and with his 
conclusions we entirely agnee. With every inward movement of the spatulate process 
of the scaphium “ the cavity of the atrium sinus imparls is diminished, and the 
contained fluid urged onward. As the result of more fluid being forced into the cavum 
sinus imparls the saccus endolymphaticus, which floats freely in it, must be compressed 
and a current of endolymph urged forwards which must impinge very directly on the 
macula acustica sacculi of each side. The position of the maculae with relation to the 
saccus and ductus endolymphaticus would appear to render unnecessary the special 
maculae described by Nusbaum (29) in Cyprinus. In any case the altered tension in the 
anterior part of the air-bladder will be brought within range of perception by the 
auditory nerve ” (43, p. 383). If any doubt attaches to these statements it is 
whether the saccus endolymphaticus undergoes actual compression, or that as a 
consequence an actual flow of endolymph takes place towards the sacculi. It may 
more probably be the case that movements of the two scaphia produce oscillation 
waves in the fluids of the atrial cavities and the cavum, and that such waves cause 
similar disturbances in the endolymph of the saccus and ductus endolymphaticus, but 
without there being any actual flow towards the sacculi. There can be but little 
doubt that the sensory epithelium of the two sacculi is solely concerned in the trans- 
mission of stimuli received through the Weberian mechanism to the auditory nerve, 
for the oblique valve in the ductus sacculo-utricularis must prevent the extension of 
any disturbance in the endolymph of the sacculi to the utriculi, or to the semi-circular 
canals and their ampullae. 
Hasse’s suggestion (18) that the propulsion of fluid into the atrial cavities and the 
cavum sinus imparis may, by radiation of pressure, directly stimulate either the spinal 
cord or the base of the brain, has been successfully opposed by Ramsay Wright, who 
expresses his belief “ that it is solely through the auditory nerve, and especially 
through its saccular branches, that the central nervous system is informed of the 
movements of the ‘ malleus ’ and ‘ stapes,’ and consequently the state of distension of 
the air-bladder” {loc. cit., p. 384). 
The peculiar sac (receptaculum dorsale) which in Amiurus catus lies on the dorsal 
side of the medulla oblongata, and ends blindly behind in two lobes but anteriorly 
communicates with each atrium at the point where the latter becomes continuous with 
the cavum sinus imparis may, as Ramsay Wright {loc. cit., p. 384) not unreasonably 
suggests, act as a reservoir for the fluids of the atrial cavities, or may serve to receive 
any excess driven out of the atria by the movements of the scaphia, and therefore 
prevent shocks of undue force from being imparted to the endolymph of the saccus 
endolymphaticus, and eventually to the nerve endings of the maculae acusticae of the 
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