PHYSIOLOGICAL ANATOMY OF THE INTERNAL EAR. 757 



canal of the cochlea and the true membranous cochlea. Viewed externally, the 

 true membranous cochlea appears as a single tube, following the turns of the 

 bony cochlea, beginning below by a blind extremity and terminating in a blind 

 extremity at the summit of the cochlea. If a section of the cochlea be made in 

 a direction vertical to the spiral, it will be seen that the bony canal is divided, 

 partly by bone and partly by membrane, into an inferior portion, a superior 

 portion, and a triangular canal, lying between the two, which is external. 

 The bony septum is in the form of a spiral plate, extending from the central 

 column (the modiolus) into the cavity of the cochlea, about half-way 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 

 central column it divides into two plates, with an intermediate, spongy struct- 

 ure, 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 out- 

 er wall of the cochlea. 

 In this way the bony coch- 

 lea is divided into two 

 portions, one above and 

 the other below the sep- 

 tum. The portion below 

 begins at the fenestra ro- 

 tunda and is called the 

 scala tympani. The por- 

 tion above, exclusive 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 spiralis, 

 the external continuation of which is called the membrana tectoria, or the 

 membrane of Corti. Between the membrana tectoria and the membrana 

 basilaris is 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 portions : an internal portion, the scala vestibuli, and an 

 external triangular canal, called the canalis cochleae, or the true membra- 

 nous cochlea. 



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

 scalae and membranous parts may be designated as follows : 



FIG. ZrQ.Otolithsfrom various animals (Riidinger). 

 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. 



