684 DISSECTION OF THE EAR. 



as the names express : the scala vestibuli opens into the front of the ves- 

 tibule (fig. 244, g") ; but the scala tympani is shut out from the vestibular 

 cavity by the lamina spiralis of the septum cochleae, and is closed below 

 by the membrane of the fenestra rotunda, though in the dry bone it opens 

 into the tympanum. 



Each has certain peculiarities. The vestibular scala extends into the 

 apex of the cochlea ; whilst the tympanic scala is largest near the base. 

 Connected with the last is the small aqueduct of the cochlea, which begins 

 close to a ridge near the lower end of the scala, and opens at the lower 

 border of the petrous portion of the temporal bone. 



The scalae are clothed with a thin fibrous membrane, continuous with 

 that in the vestibule : in the scala tympani it helps to close the fenestra 

 rotunda, forming the inner layer of the secondary membrane of the tym- 

 panum, and joins the fibrous process in the aqueduct of the cochlea. The 

 fluid of the vestibular space fills both scalae. 



SMALLER PARTITIONS OF THE COCHLEA (fig. 247). Two thin mem- 

 branes are prolonged from the septum to the outer wall, across the vestibu- 

 lar scala. One is called membrane of Reissner, and the other membrane 

 of Corti. 



The membrane of Reissner ( J ), which is easily torn, is prolonged ob- 

 liquely from the upper surface of the septum cochleae, where the limbus 

 ends, to the outer part of the tube of the cochlea, so as to cut off a small 

 channel, the canal of the cochlea (cc). It is formed by a very thin layer 

 of fine connective tissue with blood capillaries, and is covered by the epi- 

 thelial lining of the two spaces between which it intervenes. 



The membrane of Corti (me) (membrana tectoria) stretches horizon- 

 tally across the tube of the cochlea near, and parallel to the membrana 

 basilaris. Internally it is attached to the limbus of the septum cochleae, 

 and externally to the wall of the cochlear tube. It is a thin elastic trans- 

 versely-fibred layer, which is thicker internally than externally. Between 

 it and the membrana basilaris (mbj is a narrow channel for the reception 

 of the organ of Corti. 



SMALLER PASSAGES OF THE COCHLEA (fig. 247). The spaces result- 

 ing from the subdivision of the scala vestibuli by the membranes above 

 noticed are two in number, viz., canal of the cochlea, and space for the 

 organ of Corti. 



The canal or duct of the cochlea (cc) is the narrow interval towards 

 the outer part of the cochlear tube, between the membrane of Reissner ( ! ), 

 and the membrane of Corti (me). It extends from apex to base of the 

 cochlea like the larger scalae ; it is lined by epithelium, and contains a 

 fluid (endolymph). 



Above it reaches into the cupola and is closed. Below it is joined by 

 a very small tube (fig. 248, c) (canalis reuniens Hensen), with the saccule 

 in the vestibule. 



The space for the organ of Corti is a narrow interval corresponding in 

 in depth with the sulcis spiralis, and is placed between the membrane of 

 Corti (me) and the membrana basilaris (mb). It contains the organ of 

 Corti and is filled with fluid. 



The ORGAN OF CORTI (fig. 247) rests on the membrana basilaris (mb), 

 and occupies a narrow space between this and the membrane of Corti ; it 

 consists of rods and cells placed vertically on each side of a median space 

 (sm). 



The rods are firm peculiar bodies, which are arranged in two rows (d 



