VESSELS AND NERVES OF TYMPANUM. 



07 



In the foetus the mucous membrane of the tympanum consists of a swollen gela- 

 tinous embryonic tissue which fills the cavity, leaving only an irregular cleft between 

 its folds. Towards the end of intrauterine life the membrane becomes gradually 

 thinner and less gelatinous and the cleft enlarges, fluid accumulating within it. 

 After birth this fluid becomes replaced by air, and the mucous membrane speedily 

 acquires the thin fibrous character which it exhibits throughout life. 



superior ligament of malleus head of malleus 



superior external pouch .^|| 



external ligament of malleus 

 inferior external pouch (of Prussak) , 

 processus brevis mallei ''' 



external auditory meatus J 



tendon of tensor 

 t/jmpani 



manubrium mallei 

 end of manubrium 



Fig. 104. SECTION THROUGH THE MALLEUS AND MEMBRANA TYMPANI, SHOWING SOMK OF THE POUCHES 

 OR RECESSES OP THE TYMPANIC CAVITY. (After Merkel.) 



Vessels and nerves of tympanum. The arteries of the tympanum, though 

 very small, are numerous, and are derived from branches of the external carotid, 

 and from the internal carotid. 



The fore part of the cavity is supplied chiefly by the tympanic branch of the 

 internal maxillary, which enters by the fissure of Glaser. The back part of the 

 cavity including the mastoid cells, receives its arteries from the stijlo-mastoid branch 

 of the posterior auricular artery, which is conducted to the tympanum by the aque- 

 duct of Fallopius. These two arteries form by their anastomosis a vascular circle 

 round the margin of the membrana tympani. The smaller arteries of the tympanum 

 are, the petrosal branch of the middle meningeal, which enters through the hiatus 

 Fallopii, and branches through the bone from the internal caroiid artery, furnished 

 from that vessel whilst in the carotid canal. 



The veins of the tympanum empty their contents into the superior petrosal 

 sinus arid the temporo-maxillary vein. 



Nerves. The tympanum contains numerous nerves ; for, besides those which 

 supply the parts of the middle ear itself, there are several which serve merely to 

 connect nerves of different origin. 



The lining membrane of the tympanum is supplied by filaments from the 

 tympanic plexus, which occupies the shallow grooves on the inner wall of the cavity, 

 particularly on the surface of the promontory (fig. 93). 



This plexus (fig. 105) is formed by 1st, the nerve of Jacobson from the petrosal 

 ganglion of the glosso-pharyngeal ; 2nd, the small deep petrosal nerve, a filament 

 connecting the nerve of Jacobson with the carotid plexus of the sympathetic ; 3rd, 

 a branch which joins the great superficial petrosal nerve ; 4th and lastly, the small 

 superficial petrosal nerve, passing to the otic ganglion. 



Numerous ganglion cells are found both in the uniting cords and also at the 

 points of junction of the plexus. 



VOL. III., PT. 3. H 



