6/8 THE SENSE OF HEARING. 



some peculiar club-shaped little bodies called the rods of Corti, 

 set up on end, with their big extremities upwards, and leaning 

 against each other at the top a section, therefore, having 

 the appearance of the gable-end of a house. On their 

 outer part are numerous cells of various shapes. The 

 regularity with which the little rods of Corti are arranged, 

 has caused them to be compared to rows of keys in a piano. 



In close relation with these rods and the cells outside 

 them, and probably projecting also by free ends into the 

 little triangular canal containing fluid which is between 

 the rods, are filaments of the auditory nerve. 



The membranous labyrinth corresponds generally with the 

 form of the osseous labyrinth, so far as regards the vesti- 

 bule and semicircular canals, but is separated from the 

 walls of these parts by fluid, except where the nerves enter 

 into connection within it. In the cochlea, the membranous 

 labyrinth completes the septum between the two scala, and 

 encloses a separate spiral canal, the canalis membranacea. 

 As already mentioned, the membranous labyrinth contains 

 a fluid called endolymph ; and between its outer surface and 

 the inner surface of the walls of the vestibule and semi- 

 circular canals is another collection of similar fluid, called 

 perilymph : so that all the sonorous vibrations impressing 

 the auditory nerves on these parts of the internal ear are 

 conducted through fluid to a membrane suspended in and 

 containing fluid. The fluid in the scales of the cochlea 

 is continuous with the perilymph in the vestibule and 

 semicircular canals, and there is no fluid external to its 

 lining membrane. 



The vestibular portion of the membranous labyrinth 

 comprises two, probably communicating cavities, of whicli 

 the larger and upper is named the utriculus ; the lower, the 

 sacculus. Into the former open the orifices of the mem- 

 branous semicircular canals ; into the latter the canalis 

 membranacea of the cochlea. The membranous labyrinth 

 of all these parts is laminated, transparent, very vascular, 



