HEARING. 303 



signaled, from the intricacy of its winding passages, the la- 

 byrinth. It is seen at (s v K) in 

 Fig. 390, in connexion with the 

 tympanum; but in Fig. 394, it is 

 represented, on a very large scale, 

 detached from every other part, 

 and separated from the solid bone 

 in which it lies embedded. It 

 consists of a middle portion, 

 termed the vestibule (v,) from 

 which, on its upper and posterior 

 side, proceed the three tubes (x, 

 Y, z,) called, from their shape, the 

 semicircular canals; while to the lower anterior side of the 

 vestibule there is attached a spiral canal, resembling in ap- 

 pearance the shell of a snail, and on that account denomi- 

 nated the Cochlea (K.) All these bony cavities are lined 

 with a very delicate membrane, or periosteum, and are filled 

 with a transparent watery, or thin gelatinous fluid, which is 

 termed by Breschet, the perilymph* 



Within the cavity of the osseous labyrinth, now de- 

 scribed, are contained membranes having nearly the shape of 

 the vestibule and semicircular canals, but not extending into 

 the cochlea. These membranes, which compose what has 

 been termed, for the sake of distinction, the membranous 

 labyrinth, form one continuous, but closed sac, containing a 

 fluid,! perfectly similar in appearance to the perilymph, 

 which surrounds it on the outer side, and intervenes be- 

 tween it and the sides of the osseous labyrinth, preventing 

 any contact with those sides. In Fig. 395, which is on a 

 still larger scale than the preceding figure, the osseous laby- 

 rinth is laid open, so as to show the parts it encloses, and 



* Annales des Sciences Naturelles, xxix. 97. It has also been called the 

 Aqua labyrinlhi, and the fluid of Cotunnius, from the name of the Anato- 

 mist who first distinctly described it. 



| De Blainville has termed this fluid " la vitrine auditive," from its sup- 

 posed analogy with the vitreous humour of the eye. 





