THE MIDDLE EAR, DRUM, OR TYMPANUM H37 



covering the pyramid, ossicula, and membrana tympani possesses a flattened, none-mated epi- 

 thelium. In the antrum and mastoid cells its epithelium is also nonciliated. In the osseous 

 portion of the Eustachian tube the membrane is thin, but in the cartilaginous portion it is very 

 thick, highly vascular, covered with ciliated epithelium, and provided with numerous mucous 

 glands. 



Vessels and Nerves. The arteries supplying the tympanum are six in number. Two of 

 them are larger than the rest viz., the tympanic branch of the internal maxillary, which enters 

 by tvay of the petrotympanic or Glaserian fissure and supplies the memhrana tympani; and the 

 stylomastoid branch of the posterior auricular, which passes through the stylomastoid foramen 

 and the facial canal, and supplies the inner wall and floor of the tympanum, the mastoid cells 

 and antrum, and the Stapedius muscle. This vessel anastomoses around the tympanic mem- 

 brane with the tympanic. The middle meningeal sends a small branch to the Tensor tympani 

 muscle near its origin. The petrosal branch of the middle meningeal enters the tympanum by 

 way of the hiatus canalis facialis. Minute branches from the posterior branch of the middle 

 meningeal pass through the petrosquamous fissure and are distributed to the antrum and epi- 

 tympanic recess. Two tympanic branches come off from the internal carotid artery in its course 

 through the carotid canal. A branch from the ascending pharyngeal and another from the 

 Vidian accompany the Eustachian tube. The two tympanic branches from the internal carotid 

 are given off in the carotid canal and perforate the thin anterior wall of the tympanum. The 

 veins of the tympanum terminate in the pterygoid plexus, the middle meningeal vein, and the 

 superior petrosal sinus. 



The nerves of the tympanum constitute the tympanic plexus (plexus tympanicus [Jacobsoni]), 

 which ramifies upon the surface of the promontory (Fig. 839). The plexus is formed by (1) the 

 tympanic branch of the glossopharyngeal ; (2) the small deep petrosal nerve; (3) the small super- 

 ficial petrosal nerve; and (4) a branch which joins the great superficial petrosal. 



The tympanic branch of the glossopharyngeal or Jacobson's nerve (n. tympanicus) enters 

 the tympanum by an aperture in its floor close to the inner wall and divic'ec into branches, 

 which ramify on the promontory and enter into the formation of the plexus. The small deep 

 petrosal nerve (n. petrosus profundus), from the carotid plexus of the sympathetic, passes 

 through the wall of the carotid canal, and joins the branches of Jacobson's nerve. The branch 

 to the great superficial petrosal passes through an opening on the inner wall of the tympanum 

 in front of the fenestra ovalis. The small superficial petrosal nerve (n. petrosus superficialis 

 minor), derived from the otic ganglion, passes through a foramen (canaliculus innominatus) 

 in the middle fossa of the base of th'e skull (sometimes through the foramen ovale), passes 

 backward and enters the petrous bone through a small aperture, situated external to the hiatus 

 canalis facialis on the anterior surface of this bone; it then courses downward through the 

 bone, and, passing by the geniculate ganglion, receives a connecting filament from it (Fig. 845) 

 and enters the tympanic cavity, where it communicates with Jacobson's nerve, and assists in 

 forming the tympanic plexus. 



The branches of distribution of the tympanic plexus are supplied to the mucous membrane of 

 the tympanum; one special branch passing to the fenestra ovalis, another to the fenestra ro- 

 tunda, and a third to the Eustachian tube. The small superficial petrosal may be looked upon 

 as the continuation of the tympanic nerve (Jacobson's) through the plexus to the otic ganglion. 



In addition to the tympanic plexus there are the nerves supplying the muscles. The Tensor 

 tympani is supplied by a branch from the third division of the trigeminal through the otic gan- 

 glion, and the Stapedius by the tympanic branch of the facial. 



The chorda tympani (Figs. 835 and 838) crosses the tympanic cavity. It is apparently given 

 off from the facial as it passes vertically downward at the back of the tympanum, about 6 mm. 

 (a quarter of an inch) before its exit from the stylomastoid foramen. It passes from below 

 upward and forward in a distinct canal, and enters the cavity of the tympanum through an 

 aperture, iter chordae posterius, already described (p. 1128), and becomes invested with mucous 

 membrane. It passes forward, through the cavity of the tympanum, crossing internal to the 

 membrana tympaBI and over the handle of the malleus to the anterior inferior angle of the tym- 

 panum, and eme^|irf from that cavity through the iter chordae anterius or canal of Huguier 

 (p. 1128). 



Applied Anatomy. The principal point in connection with the surgical anatomy of the 

 tympanum is its relations to other parts. Its roof is formed by a thin plate of bone, which, with 

 the dura, is all that separates it from the temporal lobe of the brain. Its floor is immediately 

 above the jugular fossa and the carotid canal, the fossa being behind and the canal in front. Its 

 posterior wall presents the opening of the mastoid cells. On its anterior wall is the opening of 

 the Eustachian tube. Thus, it follows that in disease of the middle ear we may get subdural 

 abscess, septic meningitis, or abscess of the cerebrum or cerebellum from extension of the inflam- 

 mation through the bony roof; thrombosis of the lateral sinus, with or without pvemia, by ex- 

 tension through the floor; or mastoid abscess by extension backward. In addition to this, we 

 mav get fatal hemorrhage from the internal carotid in destructive changes of the middle ear: 

 and in throat disease we may get the inflammation extending up the Eustachian tube to the 



72 



