218 SPECIAL SENSES. 



The membranous cochlea, as described above, follows the 

 spiral course of the cochlea, terminates superiorly in a blind, 

 pointed extremity at the cupola, beyond the hamulus, and is 

 connected below with the saccule of the vestibule by the ca- 

 nalis reunions. The relations of the different portions of the 

 membranous cochlea to each other and to the scalse of the 

 cochlea are shown in Fig. 16. This figure also shows other 

 structures, which we shall not describe more minutely, as 

 they are of purely anatomical interest. 



We shall now describe, as possessing the most physiologi- 

 cal interest, the liquids of the labyrinth, the distribution and 

 connections of the nerves in the labyrinth, and the organ of 

 Corti. 



Liquids of the Labyrinth. The labyrinth contains a cer- 

 tain quantity of a clear, watery liquid, called the humor of 

 Cotugno, or of Yalsalva. A portion of this liquid surrounds 

 the membranous sacs of the vestibule, the semicircular ca- 

 nals, and the membranous cochlea, and this is known as the 

 perilymph of Breschet. Another portion of the liquid fills 

 the membranous labyrinth. This is sometimes called the 

 humor of Scarpa, but is known more generally as the endo- 

 lymph of Breschet. 1 The perilymph occupies about one-third 

 of the cavity of the vestibule, of the semicircular canals and 

 both scalse of the cochlea. Both this liquid and the endo- 

 lymph are clear and watery, becoming somewhat opalescent on 

 the addition of alcohol. The perilymph seems to be secreted 

 by the periosteum lining the osseous labyrinth. As far as 

 we know, the uses of the liquid of the internal ear are to 

 sustain the delicate structures contained in this portion of the 

 auditory apparatus and to conduct sonorous vibrations to the 

 terminal filaments of the auditory nerves and the parts with 

 which they are connected. 



Distribution of the Nerves in the Labyrinth. As the 



1 BRESCHET, Reclierches anatomiques et physiologiques sur Vorgane de Fouie et 

 sur Vaudition, Paris, 1836, pp. 51, 56. 



