1538 A MANUAL OF ANATOMY 



Middle Ear. 



The middle ear, or tympanum, is an irregular space within the 

 petrous part of the temporal bone, which lies between the mem- 

 brana tympani externally and the outer osseous wall of the internal 

 ear or labyrinth internally. It is lined with mucous membrane, and it 

 communicates with the naso-pharynx by means of the Eustachian 

 tube, through which it receives air. It presents three parts, namely, 

 (i) the t5niipanum proper, or cavum t)mipani ; (2) the attic, or epi- 

 tympanic recess ; and (3) the tympanic or mastoid antrum. 



The tympanum proper, or cavum tympani, is situated between 

 the membrana tympani and the outer wall of the internal eaj. Its 

 contents are as follows : 



I. A chain of ossicles (malleus, 2. Muscles, 



incus, and stapes), with 3. Nerves. 



their ligaments. 4. Bloodvessels. 



The vertical and antero-posterior diameters (inclusive of the 

 attic) are fully | inch. The transverse measurement is from 

 I to 1^ inch, except opposite the centre of the membrana t5mipani,. 

 where it is only Yt inch. 



The tympanic cavity presents six walls — outer, inner, roof, fioor,^ 

 anterior, and posterior. 



The outer wall is formed (i) chiefly by the membrana tympani, 

 which has the handle of the malleus fixed to it, and (2) slightly by 

 the tympanic annulus, within the circumference of which there is 

 a groove, called the sulcus tympanicus, in which the membrana 

 tympani is set. The tympanic annulus and sulcus are interrupted 

 superiorly by a notch, called the notch of Rivini. In front of the 

 tympanic annulus is the open, inner extremity of the fissure of 

 Glaser, which lodges the processus gracilis of the malleus, and trans- 

 mits the tympanic branch of the internal maxillary artery. At 

 the inner end of the fissure of Glaser is the opening of the iter 

 chordcB anterius, or canal of Huguier, by which the chorda tympani 

 nerve leaves the tympanum. 



The inner wall separates the tympanum from the internal ear or 

 labyrinth. It is very irregular, and presents the following parts : 



1. The fenestra ovalis. 3. The promontory. 



2. Projection formed by part of the 4. The fenestra rotunda. 



aqueduct of Fallopius. 5. The sinus tympani. 



The fenestra ovalis is situated in a depression, called the fossula 

 ovalis, at the upper part of the inner wall, and it leads into the cavity 

 of the vestibule. It is irregularly oval, and is elongated from before 

 backwards. It is occupied by the footpiece of the stapes, and the 

 annular ligament which connects the circumference of the footpiece 

 to the margin of the opening, the margin being covered by cartilage. 



The projection formed by part of the aqueduct of Fallopius is 

 situated above the fenestra ovalis. The aqueduct, which contains 

 the facial nerve, is here directed backwards. 



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