CHAP. XVIII.] THE INNER WALL OF THE TYMPANUM. 69 



The inner layer is the ciliated epithelial lining of the cavity, which 

 is easily scraped off for examination in the fresh state (see vol i 

 p. 62). 



Fig. 132. 



Diagram of the inner wall of the tympanum after maceration, the outer wall and ossicles 

 being removed. . Fenestra ovalis. b. Fenestra rotunda, c. Promontory, d. Pyramid, with 

 the orifice at its apex. e. Projection of the aqueductus Fallopii. /. Some of the mastoid cells 

 communicating with the tympanum, g. Processus cochleariformis, bounding , the canal for 

 the tensor tympani muscle : the anterior pyramid is broken off, if it existed, h. Commence- 

 ment of the Eustachian tube. j. Jugular fossa, immediately below the tympanum, k, k. Caro- 

 tid canal, with the artery in outline, to show its course in relation to the tympanum and Eusta- 

 chian tube. /. Portio dura of the seventh pair of nerves, as it would be seen in the terminal 

 part of the aqueduct of Fallopius. m. Chorda tympani, leaving the portio dura, and entering 

 a short canal, which opens in the tympanum, at the base of the pyramid, n. Grooves for the 

 tympanic plexus. 



The internal wall of the tympanum (fig. 132) has two orifices of 

 communication with the internal ear; the fenestra ovalis, a, leading 

 to the vestibule, and the fenestra rotunda, b, opening into the 

 cochlea. Both these are closed by membrane which prevents the 

 escape of the fluid contained in these inner chambers, and communi- 

 cates vibrations to it. The fenestra ovalis is likewise occupied by 

 the base of the stapes, one of the chain of ossicles connecting it with 

 the membrana tympani. Between the fenestrse is the promontory, c, 

 corresponding to the first turn of the cochlea, and furrowed by two or 

 three canals for the nerves which form the anastomosis of Jacob son, n. 

 Behind the fenestra ovalis is a conical eminence, the pyramid, d, hol- 

 lowed, and presenting a small orifice at its summit, \vhich is on a 

 level with the middle of the vestibular fenestra. The pyramid con- 

 tains the stapedius muscle, the tendon of which emerges at its sum- 

 mit, and runs to the neck of the stapes. This muscle is supplied 



