746 SPECIAL SENSES 



The membranous cochlea, as just described, includes the scala 

 media and the quadrilateral canal, follows the spiral course of the coch- 

 lea, terminates superiorly in a pointed blind 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 por- 

 tions of the membranous cochlea to each other and to the scalae of the 

 cochlea also are shown in Fig. 193. 



Liquids of the Labyrinth. The labyrinth contains a certain quan- 

 tity of a clear watery liquid, called the humor of Cotugno or of Valsalva. 

 A portion of this liquid surrounds the utricle and saccule, the semicircu- 

 lar canals and the true membranous cochlea ; and this is known as the 

 perilymph of Breschet. Another portion of the liquid fills the true 

 membranous labyrinth and is sometimes called the humor of Scarpa; 

 but it is known more commonly as the endolymph of Breschet. The 

 perilymph occupies about one-third of the cavity of the bony vestibule 

 and semicircular canals and both scalae of the cochlea. Both this liquid 

 and the endolymph are clear and watery, becoming somewhat opales- 

 cent on the addition of alcohol. The spaces in the labyrinth are directly 

 connected with the lymphatic system. The space occupied by the peri- 

 lymph communicates with lymphatics chiefly through the aqueduct of 

 the cochlea, but there also is a communication through the internal 

 auditory meatus with the space beneath the dura mater. The endo- 

 iymph passes to the subarachnoid space beneath the arachnoid covering 

 of the auditory nerve. So far as is known, the uses of the liquid of the 

 internal ear are to sustain the delicate structures contained in this por- 

 tion 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 internal auditory meatus, they divide into an anterior, or coch- 

 lear, and a posterior, or vestibular branch. The vestibular branch di- 

 vides 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 semicircu- 

 lar canal. The nerves distributed to the utricle and saccule penetrate 

 at the points occupied by the otoliths, and the nerves going to the semi- 

 circular canals pass to the ampullae, which also contain otoliths (see 

 Fig. 191). 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 transversum. 



