CALCAREOUS CONCRETIONS IN THE LABYRINTH. 475 



the lymph, at opposite points in the labyrinth, which should 

 pass once through different portions of the labyrinth, agitate 

 all the parts on which the nerves are spread, and finally neu- 

 tralise each other in the semicircular canals and in the scala of 

 the cochlea, so as to prevent the repetition and reverberation 

 of single sounds. 



The calcareous concretions above alluded to, are found, in 

 the mammiferse, only in the alveus communis and sacculus 

 ellipticus of Scarpa, in which the semicircular tubes open, and 

 which Breschet calls the middle sinus. They form a small 

 single granular mass. Opposite these concretions the auditory 

 nervous filaments terminate in great number, and the promi- 

 nent villi which they form seem even to reach the concretions. 

 Gregoire St. Hilaire and Breschet, have instituted compari- 

 sons between the parts of the labyrinth which form the organ 

 of hearing proper, and the parts contained in the globe of the 

 eye. The endolymph they call the vitrine auditive, and con- 

 sider it functionally analogous to the vitreous humor of the eye, 

 in allowing the sonorous rays or impulses to pass through it, and 

 in keeping distended the membranous labyrinth upon which the 

 nerves terminate, and which they consider analogous to the 

 retina. The light calcareous concretions are, as they think, for 

 the purpose of increasing the effect of the impulses, as the cry- 

 stalline humor increases the effect of the luminous rays by con- 

 centrating them into a focus. Arnold and Tiedemann consider 

 the rnembrana tympani as analogous in its office to the iris, regu- 

 lating, by its state of tension or relaxation, the degree of impres- 

 sion made upon the nerves of hearing. This comparison is ren- 

 dered more complete, by the recent discovery by Arnold, of an 

 auricular ganglion, which is considered as an appendage of the 

 sympathetic nervous system, and which, according to them, is 

 as much the central regulator of the sympathetic or instinctive 

 movements of the membrana tympani, as the ophthalmic gang- 

 lion is of that of the iris. 



y, y, Bristle lodged in the infundibulum (HeHcotrome,) by which the two scala 

 communicate together at the top of the modiolus. z, Place where the modio- 

 lus is continuous at its summit, with the walls of the osseous labyrinth, rv, TV, 

 re, Membranous portion of the lamina spiralis. 



