472 COCHLEA. 



in the vestibule, and to the membranous semicircular canals ; 

 so that the membranous labyrinth rnay be said to be immersed 

 in a fluid. 



This fluid fills, also the cochlea. 



A useful distinction has been made by many anatomists 

 of the parts of the labyrinth or internal ear, into a bony laby- 

 rinth and a membranous labyrinth. The bony labyrinth, 

 consisting of the bony vestibule, cochlea, and semicircular 

 canals, forms only the frame-work or walls to more important 

 parts. The sacs of the vestibule, the membranous lining of the 

 cochlea, and the membranous semicircular tubes, are the parts 

 upon which the auditory nerves and vessels are distributed, and 

 form the structures immediately concerned in the production of 

 hearing. The membranous cochlea, so far at least as has yet 

 been observed, lines the internal face of the scala of the bony 

 cochlea, and appears to serve as its periosteum as well as a 

 field for the expansion of the cochlear division of the auditory 

 nerve. The vestibule and the semicircular canals have a perios- 

 teal lining membrane distinct from their membranous structure 

 and from which the limpid fluid of the labyrinth is secreted. 

 The membranous sac of the vestibule, and the membranous 

 canals, occupy but a small part of their respective bony cavi- 

 ties, with the walls of which, according to the recent researches 

 of Breschet, they are only indirectly connected by the nerves 

 and blood-vessels which enter their structure through foramina 

 in the bony labyrinth. The limpid fluid alluded to, (p. 410,) 

 called the lymph of Cotunnius, from the anatomist who first 

 described it, is found not only filling the cavities of the mem- 

 branous labyrinth, but likewise fills up completely the space 

 between the membranous and bony vestibule, and the mem- 

 seen accompanying all these branches, e, A venous sinus, excavated in the 

 bone, at the outer margin of the zona membranosa. The venus sinus e, opens at 

 the margin of the lamina spiralis, which divides the scala tympani below from 

 the scala vestibuli above. Between the windings of the double tube, which 

 resemble the turns of a circular pair of stairs, is seen a process of bony mat- 

 ter passing in to the modiolus. The bristle is passed in at the infundibulum, 

 through the scala tympani, and brought out through the scala vestibuli, show- 

 ing the communication of these cavities. 



