CHAP. XVIII.] OFFICE OF THE LABYRINTH. 97 



could by means of a sounding-rod applied in succession to the mem- 

 brane of each of the artificial fenestrse ascertain the relative intensity 

 of the sonorous vibrations communicated to the water through the 

 two openings, while another person sounded the pipe. He states 

 that the difference was very striking. The sound transmitted by 

 the wooden rod to the opening which represented the fenestra 

 ovalis was in a remarkable degree louder than that propagated 

 through the air of the cavity to the membrane of the other opening. 



The results of this experiment lead to the conclusion (which 

 other circumstances confirm), that the vestibule is adapted to re- 

 ceive sounds from 'the tympanic membrane and external ear, while 

 the cochlea is not easily affected in this manner, but rather, as its 

 structure and connexions point out, that it is fitted to receive vibra- 

 tions through the bones of the head. 



The direct continuity of the walls and the septum ( lamina spira- 

 lis) of the cochlear canal, with the petrous bone, and the minute 

 subdivision of the nerve in distinct canals in the osseous substance, 

 render that portion of the labyrinth most readily affected by the vi- 

 brations excited in the cranial bones. The cochlea may therefore 

 be properly considered as that part of the labyrinth which is more 

 immediately affected by sounds communicated through the bones of 

 the head, as the vestibule is the part primarily affected by the 

 sounds communicated through the external ear. 



It may be easily shown by some experiments with the tuning- 

 fork, not only that the cranial bones do conduct, but also that 

 sounds inaudible, or imperfectly audible, through the meatus externus 

 may be distinctly heard when the sounding body is brought into 

 contact with a bone of the cranium or face. When the tuning- 

 fork is thrown into vibration by striking it against any solid body, 

 if held near the external ear its vibrations are distinctly heard, but 

 let the stem be applied to the teeth, or to the upper jaw, or to the 

 parietal bone, and the sound appears much louder; or if the fork be 

 held near the ear until the sound has almost died away, and then 

 its stem be applied to the superior maxilla, or to the teeth, the sound 

 seems to revive, and continues for a considerable period while the 

 stem is kept in contact with the bone. 



The form of the cochlea probably has reference to the convenient 

 package within the smallest compass of the great number of nerve- 

 fibres which proceed to it. 



The remarkable subdivision which the cochlear nerve undergoes, 

 admirably adapts it for the reception of vibrations communicated 

 through the cranial bones. ' ' The spiral lamina of the cochlea," says 



VOL. II. H 



