8 46 SPECIAL SENSES. 



larger, and a quadrilateral canal below, between the limbus and membrana tectoria and 

 the membrana basilaris. The quadrilateral canal contains the organ of Corti and various 

 structures of a very complicated character. The relations of these divisions of the cochlea, 

 a knowledge of which is essential to the comprehension of the physiological anatomy of 

 this portion of the auditory apparatus, are shown in Fig. 266. 



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 canalis reuniens. The 

 relations of the different portions of the membranous cochlea to each other and to the 

 scalae of the cochlea are shown in Fig. 266. 



We shall now describe, as possessing the most physiological 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 certain quantity of a clear, 

 watery liquid, called the humor of Cotugno, or of Valsalva. A portion of this liquid 

 surrounds the membranous sacs of the vestibule, the semicircular canals, and the mem- 

 branous 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 it is known more generally as the endolymph of Breschet. The perilymph occupies 

 about one-third of the cavity of the vestibule, of the semicircular canals, and of both scales 

 of the cochlea. Both this liquid and the endolymph 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 auditory nerves enter the inter- 

 nal auditory meatus, they divide into an anterior, or cochlear, and a posterior, or vestib- 

 ular branch. The vestibular branch divides into three smaller branches, a superior and 

 anterior, a middle, and a posterior branch. The superior and anterior branch, the largest 

 of the three, is distributed to the utricle, the superior semicircular canal, and the external 

 semicircular canal. The middle branch is distributed to the saccule. The posterior 

 branch passes to the posterior semicircular canal. The nerves distributed to the utricle 

 and saccule penetrate at the points occupied by the otoliths, and the nerves going to the 

 semicircular canals pass to the ampulla), which also contain otoliths. (See Fig. 264.) In 

 each ampulla, at the point where the nerve enters, is a transverse fold, projecting into 

 the canal and occupying about one-third of its circumference, called the septum trans- 

 versum. 



The nerves terminate in essentially the same way in the sacs of the vestibule and the 

 ampullae of the semicircular canals. At the points where the nerves enter, in addition 

 to the otoliths, are cells of cylindrical epithelium, of various forms, which pass gradually 

 into the general pavement-epithelium of the cavities. In addition to these cells, are fusi- 

 form, nucleated bodies, the free ends of which are provided with hair-like processes, 

 called fila acustica. These are about ^ of an inch in length and are distributed in 

 quite a regular manner around the otoliths. The nerves form an anastomosing plexus 

 beneath the epithelium, and they probably terminate in the fusiform bodies just described 

 as presenting the fila acustica at their free extremities. In the sacs of the vestibule 

 and in the semicircular canals, nerves exist only in the macula acustica and the 

 ampullae. 



The cochlear division of the auditory nerve breaks up into numerous small branches, 

 which pass through foramina at the base of the cochlea, in what is called the tractus 



