r 



THE INTERNAL EAR OR LABYRINTH 775 



fenestra ovalig could not vibrate properly, because it could not over- 

 come the high resistance resident in this chamber. 



The Membranous Canal of the Cochlea. — It has just been shown 

 that the osseous canal of the cochlea is bisected by the spiral lamina 

 and the basilar membrane attached thereto. Directly above the 

 membranous part of this partition, a second membrane stretches ob- 

 liquely across the lumen of the vestibular scala which thus cuts off an 

 angular space, known as the central canal of the cochlea or scala media. 

 The lower boundary of the latter is formed by the basilar membrane 

 (lamina basilaris), its outer boundary by the bony wall of the cochlea, 

 and its upper by the aforesaid membrana vestibularis or membrane of 

 Reissner. This space is filled with endolymph and forms, there- 

 fore, the cochlear continuation of the membranous labyrinth. Special 





i^^ ;/«^ 



<^ 





Fig. 393. — The Organ of Corti in the Guinea Pig. (Nakamura.) 



attention, however, should be directed to the colony of modified cells 

 situated upon the basilar membrane, the free surfaces of which 

 border upon the endolymph of this tubule. These cells form the organ 

 of Corti which is rnost directly concerned with the reception of the 

 sound waves in the form of vibrations of the lymph filling these scalse. 

 The manner in which this transfer is effected will be more fully dis- 

 cussed later on. 



The Structure of the Organ of Corti. — The basilar membrane 

 forming the floor of the central canal of the cochlea, gradually increases 

 in width from the base to the apex of the cochlea. The width of the 

 osseous lamina, on the other hand, decreases in a corresponding 

 measure. Thus, Henson^ states that its breadth amounts to only 

 about 0.041 mm. below, but to 0.495 mm. above. Its total length 

 measures 33.5 mm. Its substance is formed by a homogeneous ground- 

 substance containing numerous straight fibers which are suspended 

 in a radial manner between the tip of the bony lamina and the liga- 



1 Archiv fiir Ohrenheilkunde, vi, 1873. 



