640 



THE EAE. 



VESSELS AND NERVES OF THE TYMPANUM, 



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

 are derived from branches of the external, and from the internal carotid. 



The fore part of tlie cavity is supplied chiefly by the tymimnic branch of the in- 

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

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

 the posterior auricular artery, which is conducted to the tympanum by the 

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

 circle round the margin of the membrana tjanpani. The smaller aii;eries of the 

 tympanum are, the jwtrosal branch of the middle meningeal, which enters 

 through the hiatus FaUopVi ; branches through the bone from the internal 

 carotid artery, fm-nislied from that vessel whilst in the carotid canal ; and 

 occasionally a twig along the Eustachian tube iiova. t\ie asccndinrj phari/ngcal 

 artery. 



The veins of the tympanum empty their contents through the middle menin- 

 geal and pharjTigeal veins, and through a plexus near the articulation of the 

 lower jaw, into the internal jugular vein. 



Nerves. — The tympanum contains nnmerous 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. 



The tympanic plexus (fig. 451) is formed by the communications 

 between, 1st, the tympanic branch (nerve of Jacobson) from the petrous 

 ganglion of the glosso-pharyngeal ; 2nd, a filament from the carotid 

 plexus of the sympathetic ; 3rd, a branch which joins the gi-eat super- 

 ficial petrosal nerve ; 4th and lastly, the small superficial petrosal nerve, 

 from the otic ganglion. 



Numerous ganglion cells are present both in the uniting cords and 

 also at the points of junction of the plexus. 



Fig. 451. 



Fig. 451. — View of thk Tympanic Plexus 

 o? Nerves (after Hirschfeld and Le- 

 veiUe). 



6, spheno -palatine ganglion ; 1. Vidian 

 ners'e ; 8, great superficial petrosal nei-ve ; 

 9, carotid branch of the Vidian nerve ; 10, 

 part of the sixth nerve connected by twigs 

 with the sympathetic ; 11, superior cervical 

 ganglion of the sj-mpathetic ; 12, carotid 

 branch ; 13, facial nerve ; 14, glosso- 

 pharyngeal nerve ; 15, nerve of Jacobson ; 

 16, its twig to the sympathetic ; 17, fila- 

 ment to the fenestra rotunda ; IS, filament 

 to the Eustachian tube ; 19, filament to 

 the fenestra ovalis ; 20, union of external 

 deep petrosal nerve with the lesser super- 

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



Tlie nerve of Jacobson (fig. 451, 15) 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 fossa. The nerve from the carotid plexus is above 

 and in front of this, and passes through the bone directly from the carotid canal. 

 Tlie branch to the great superficial petrosal nerve (fig. 451. 21) is lodged m a 

 canal which opens on the inner wall of the tj-mpanum in front of the fenestra 



