564 THE NERVOUS SYSTEM. 



ing to Buck,* it is probable that no such opening exists in the natural 

 condition of the parts, unless it be microscopic in size. But whether 

 the canals communicate or not at this point, the partition between them 

 is partly membranous throughout ; and by this means any increase or 

 diminution of pressure at the fenestra ovalis will be transmitted, through 

 the scala vestibuli and scala tympani, to the membrane of the fenestra 

 rotunda, this provides therefore for the movement of the stapes, not- 

 withstanding the incompressible nature of the fluid of the labyrinth. 



But the septum formed by the spiral lamina and membrana basilaris 

 is not the only longitudinal partition in the cochlea. The scala vesti- 

 buli is also divided into two parallel canals, an internal and an external, 

 by a thin membranous sheet, which starts from the upper surface of the 

 spiral lamina near its outer border, and extends upward and outward 

 to the external wall of the cochlear cavity. As this membrane leaves 

 the spiral lamina at an angle of 45 or 50 degrees, it shuts off from the 

 scala vestibuli a separate canal of prismatic form, having for its floor 

 the membrana basilaris, for its outer wall the wall of the cochlea, and 

 for its upper boundary the oblique membranous partition above de- 

 scribed. This canal contains the auditory epithelium and the terminal 

 fibres of the auditory nerve. It is therefore the essential part of the 

 cochlea, and is termed the ductus cochlearis. 



The ductus cochlearis terminates at its apex by a blind extremity ; 

 but at its base it communicates, by a narrow channel, with the cavity 

 of the sacculus. It is consequently an extension of the sacculus, and 

 part of the membranous labyrinth ; while the scala vestibuli belongs 

 to the general cavity of the vestibule. The ductus cochlearis may be 

 considered as a tubular prolongation of the sacculus, rolled upon itself 

 in a spiral form, and held in position by the adjacent parts of the 

 cochlea. Like the rest of the membranous labyrinth, it is filled with 

 a watery fluid, and surrounded by the perilymph, except where it is 

 adherent to the walls of its bony cavity. 



Organ of Gorti. The ductus cochlearis is lined with pavement epi- 

 thelium, except along the middle of the membrana basilaris. Here 

 there is a continuous elevated ridge, four or five times thicker than the 

 epithelium elsewhere, consisting of enlarged and modified l epithelium 

 cells, and containing the terminal fibres of the auditory nerve. This 

 body is named the organ of Gorti ^ from the observer by whom it was 

 first described. It is justly considered as the most remarkable structure 

 in the internal ear, although in its essential features analogous to the 

 auditory spots of the sacculus and utricle. 



The organ of Corti rests upon the upper surface of the membrana 

 basilaris. Its framework consists of a series of elongated, rafter-like 

 bodies, arranged in two rows, internal and external. These bodies, the 



* On the Mechanism of Hearing. Prize Essay of the Alumni Association of the 

 College of Physicians and Surgeons, New York. New York Medical Journal, June, 

 1874. 



f Zeitschrift fur wissenschaftliche Zoologie. Leipzig, 1851, Band iii., p. 109. 



