SENSE ORGANS AND SENSATIONS 



257 



of these connections of the middle ear with the throat, on 

 the one hand, and with the temporal sinuses on the other, 

 inflammatory processes in. the nose and throat during a cold 

 sometimes extend into the Eustachian tube, the tympanum, 

 and even into the temporal sinuses, causing serious trouble 

 and occasionally deafness. 



Passing directly across the tympanum, from the drum on 

 its outer side to the cochlea on its inner side, is a chain of 

 three very small bones, the ear 

 ossicles (hammer, anvil, and stir- 

 rup). These bones are bound 

 together and attached to the 

 walls of the tympanum by liga- 

 ments, and are so arranged that 

 when sound waves set the tym- 

 panic membrane in vibration 

 this motion is transmitted by 

 the ossicles to a portion of the 

 inner ear known as the cochlea. 



20. The inner ear. The struc- 

 tures, of the inner ear lie in 

 the temporal bone, on the side 

 of the tympanum opposite the 

 drum. They consist of a system 

 of small bony spaces and tubes, 

 the ~bony labyrinth, within which lies a corresponding membra- 

 nous labyrinth. Forming part of the lining of the membranous 

 labyrinth are very sensitive cells, and between these cells 

 are the endings of the nerve fibers which connect the ear 

 with the brain. The cells of the inner ear are sensitive to 

 the vibrations which have been transmitted across the tym- 

 panum by the ossicles, just as the retina is sensitive to 

 light; and as the retina is the origin of the fibers of the 

 optic nerve, so the inner ear is the origin of those of the 

 auditory nerve. 



FIG. 101. The bony labyrinth, its 



actual size being shown in the 



smaller figure 



B, (7, D, the semicircular canals; 

 A, the oval window, by means of 

 which the vibrations of the stirrup 

 bone are transmitted to the cochlea ; 

 E, F, G, the whorls of the cochlea. 

 Cf . Fig. 102 



