Bauhaus-Universität Weimar

766 
THE VESTIBULE AND SEMICIRCULAR CANALS. 
with the internal periosteum of the labyrinth. (Muller's Archiv. 1834, 
p. 22.) 
There are three grades of development of the labyrinth: 1, a mere 
vestibule with a sacculus; 2, a vestibule with semicircular canals, and 
a membranous labyrinth of correspondent form; 3, the preceding parts 
with the cochlea. 
Vestibule, semicircular canals.—The function itsually ascribed to the 
semicircular canals is that which Scarpa attributed to them; namely, 
the collecting of the sonorous undulations from the bones of the cra¬ 
nium. Canals generally influence sound by the resonance of their con¬ 
tents, by the condensed propagation of the sonorous undulations in 
their interior, and by the resonance of their walls. 
No influence can be attributed to the canals of the labyrinth as re¬ 
sulting from the resonance of their contents; for water bounded by solid 
bodies is capable of perhaps no perceptible resonance, its undulations 
not being reflected by its surfaces when thus bounded. Water seems to 
be little adapted, also, for collecting sonorous undulations from sur¬ 
rounding solid bodies. 
It may therefore be inferred, that though the semicircular canals have 
probably in some degree the power of conducting sounds in the direction 
of their curve, yet this conducting power is in them much less perfect 
than in tubes containing air. Some slight increase of intensity of the 
impression on the nerve of hearing, will result from the circumstance 
that the same undulation which enters one extremity of a semicircular 
canal from the vestibule will return with a part of its force by the other 
extremity. Dr. Young has ascribed some importance to this circum¬ 
stance. 
This degree of reinforcement of the impression of hearing by means 
of the semicircular canals, will take place even when the impulse is 
communicated to the labyrinth, not through the fenestræ, but by the 
cranial bones, as in fishes, and partly in man. 
The resonance of the bony walls of the semicircular canals, excited 
by sonorous undulations in their fluid contents, comes next under con¬ 
sideration. It is found that when sonorous vibrations are imparted to 
solid surfaces in contact with water, the sound is, cæteris paribus, 
always heard with greater intensity near these surfaces than in other 
parts of the fluid; in an experiment to verify this fact, the conducting- 
rod of course must not actually touch the solid surface. If two such 
w/ 
resounding surfaces are situated very near to each other, the sonorous 
undulations of the water between them have necessarily greater inten¬ 
sity. 
If, then, we admit that the membranous semicircular canals have the conditions 
requisite for collecting the sonorous undulations of the cranial bones in their fluid con¬ 
tents, and for conducting them through their curved cavity more readily than they are 
carried off by the surrounding hard parts in the original direction of the undulations 
or impulses, the increased intensity of the sonorous vibrations thus attained will be of 
advantage in acting on the auditory nerve where it is expanded in the ampullae of the 
canals, and in the sinus communis. Where the membranous canals are in contact 
with the solid parietes of the tubes, this action must be much more intense. But the 
membranous semicircular canals must have a function independent of the surrounding 
hard parts; for in the Petromyzon they are not separately enclosed in solid substance,
        

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