182 OKGANS OF SENSE. 



mode of distribution of the vessels and nerves of the 

 external ear. 



Middle ear. The mucous membrane of the middle ear is very 

 thin ; in the Eustachian tube only it is somewhat 

 thicker. From the bony walls of the cavity it is 

 reflected upon the inner surface of the membrana 

 tympani to which it is closely adherent, and upon 

 the muscles and ossicula, for which it forms a perios- 

 teal investment. Its epithelium is everywhere cili- 

 ated, except upon the internal surface of the mem- 

 l)rana tympani, where, according to Kolliker, it' forms 

 a simple tessellated layer. 



The membrana tympani consists of a fibrous ex- 

 pansion made up of radiating and circular fasciculi, 

 and inserted by its circumference into the groove of 

 the temporal bone like a watch crystal into its case ; 

 we are familiar with the relation of its internal sur- 

 face to the mucous lining of the tympanum ; its ex- 

 ternal surface receives a layer of epidermis from the 

 walls of the meatus auditorius externus. 



The blood-vessels of the middle ear are numerous ; 

 they form a rich network in the substance of its mu- 

 cous membrane, and in the membrana tympani. The 

 lymphatic vessels probably accompany its arteries 

 and veins. 



The nerves of the middle ear come from the fifth, 

 seventh, and ninth* pairs of cranial nerves; their 

 mode of termination is unknown ; Kolliker describes 

 masses of ganglionic cells as existing in the substance 

 of the tympanic nerve. 

 internal ear. The bony walls of the semicircular canals, vesti- 



* According to the classification of Scemmering. 



