752 THE EAR. 



tube, however, this membrane becomes gradually thinner. In the tympa- 

 num and the mastoid cells it is paler, thinner and less vascular, and secretes 

 a less viscid, but yellowish fluid. The epithelium in the tympanic cavity is 

 also ciliated. The cilia, however, are usually absent from the part which 

 lines the meinbrana tympani (Kolliker, Handbuch, p. 691). 



THE VESSELS AND NERVES OF THE TYMPANUM. 



The arteries of the tympanum, though xery small, are numerous, and 

 are derived from several branches of the external, and from the internal 

 carotid. 



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

 maxillary (p. 356), which enters by the fissure of Glaser. The back part of the 

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

 of the posterior auricular aitery (p. 353), which is conducted to the tympanum by the 

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

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

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

 Fallopii ; branches through the bone from the internal carotid artery, furnished from 

 that vessel whilst in the carotid canal; and occasionally a twig along the Eustacliian 

 tube from the ascending pharyngeal artery. 



The veins of the tympanum pour their.contents through the middle meningeal and 

 pharyngeal veins, and through a plexus near the articulation of the lower jaw, into the 

 internal jugular vein. 



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

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

 merely to connect nerves of different origin. 



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

 plexus (tympanic plexus), which occupies the shallow grooves on the inner 

 wall of the cavity, particularly on the surface of the promontory. 



The tympanic plexus is formed by the communications between, 1st, the 

 tympanic branch (nerve of Jacobson) from the petrous ganglion of the glosso- 

 pharyugeal ; 2nd, & filament from the carotid plexus of the sympathetic ; 3rd, 

 a branch which joins the great superficial petrosal nerve, from the Vidian ; 

 4th and lastly, the small superficial petrosal nerve, from the otic ganglion. 



Fi S- 506 - Fig. 506. VIEW OP THE TYAIPANIO 



PLEXUS OP NERVES (after Hirschfeld 

 and Leveille). 



6, spheno-palatine ganglion ; 7, Vidian 

 nerve ; 8, great superficial petrosal 

 n?rve ; 9, carotid branch of the Vidian 

 nerve ; 10, part of the sixth nerve con- 

 nected by twigs with the sympathetic ; 

 11, superior cervical ganglion of the 

 sympathetic ; 12, carotid branch ; 13, 

 facial nerve ; 14, glosso-pharyngeal 

 nerve ; 15, nerve of Jacobsou ; 16, its 

 twig to the sympathetic ; 17, filament 

 to the fenestra rotunda ; 18, filament to 

 the Eustachian tube ; 19, filament to the 

 fenestra ovalis ; 20, union of external deep petrosal nerve with the lesser superficial 

 petrosal ; 21, internal deep petrosal twig uniting with the great superficial petrosal. 



The nerve of Jacobson enters the tympanum by a small foramen near its floor, 

 which forms the upper end of a short canal in the petrous portion of the temporal 

 bone, beginning at the base of the skull between the carotid foramen and the jugular 



