744 



SPECIAL SENSES 



cochlea, about halfway to its external wall, and terminating above in a 

 hook-shaped extremity called the hamulus. The free edge of this bony 

 lamina is thin and dense. Near the modiolus it divides into two plates, 

 with an intermediate spongy structure, in which are lodged vessels and 

 nerves. The surface of the bony lamina looking toward the base of the 

 cochlea is marked by a number of regular transverse ridges. 



Attached to the free margin of the bony lamina is a membrane, the 

 membrana basilaris, which extends to the outer wall of the cochlea. In 



this way the bony coch- 

 lea is divided into two 

 portions, one above and 

 the other below the 

 septum. The portion 

 below begins at the 

 fenestra rotunda and is 

 called the scala tympani. 

 The portion above, ex- 

 clusive of the triangular 

 canal of the cochlea, 

 communicates with the 

 vestibule and is called 

 the scala vestibuli. 



Above the membrana 

 basilaris is a membrane, 

 the limbus laminae spi-> 

 ralis, the external con- 

 tinuation of which is 

 called the membrana 

 tectoria, or the mem- 

 brane of Corti. Between the membrana tectoria and the membrana 

 basilaris is the quadrilateral canal, which contains the organ of Corti. 

 The membrane of Reissner extends from the inner portion of the limbus 

 upward and outward to the outer wall of the cochlea. This divides the 

 portion of the cochlea situated above the scala tympani into two por- 

 tions : an internal portion, the scala vestibuli, and an external triangular 

 canal, called the canalis cochleae, or the true membranous cochlea. 



In the anatomical description of the contents of the bony cochlea, 

 the scalae and membranous parts may be designated as follows : The 

 canalis cochleae is divided, as just indicated, by the membrana tectoria. 

 The portion between the membrana tectoria and the membrane of 

 Reissner is called the scala media. This communicates with the sac- 

 cule by the canalis reuniens. 



Fig. 192. Otolithsfrom various animals (Riidinger). 



i, from the goat ; 2, from the herring ; 3, from the devil-fish ; 

 4, from the mackerel ; 5, from the flying-fish ; 6, from the pike ; 

 7, from the carp ; 8, from the ray ; 9, from the shark ; 10, from 

 the grouse. 



