346 



LECT. XIX. 



must, however, presume, that you have already acquired 

 this knowledge ; and we purpose devoting the present lec- 

 ture to the study of the sense of hearing, and more especially 

 of the propagation of the sonorous vibrations through the 

 different parts of the ear. 



Structure of the Ear. But we must not pass over in 

 complete silence the structure of the ear, which varies 



Fig. 30. 



A diagram of the ear. p. The pinna, t. The tympanum. /. The labyrinth. I. 

 The upper part of the helix. 2. The antihelix. 3. The tragus. 4. The antitragus. 

 .5. The lobuliis. 6. The concha. 7. The upper part of the fossa innominata. 8. The 

 mealus. 9. The membrani tympani, divided by the section. 10. The three little 

 bones, crossing the area of the tympanum, malleus, incus and stapes ; the foot of the 

 stapes blocks up the fenestra ovalis upon the inner wall of the tympanum. 11. The 

 promontory. 12. The fencstra rotunda; the dark opening above the ossicula leads 

 into the mastoid cells. 13. The Eustachian tube ; the little canal upon this tube 

 contains the tensor tympani muscle in its passage to the tympanum. 14. The vesti- 

 bule. 15. The three semi-circular canals, horizontal, perpendicular, and oblique. 

 16. The ampullae upon the perpendicular and horizontal canals. 17. The cochlea. 

 18. A depression between the convexities of the two tubuli which communicate with 

 the tympanum and vestibule; the one is the scala tympani, terminating at 12; and 

 the other is the scala vestibuli. 



