THE SENSES. 277 



without inwards, from above downwards, and from behind for- 

 wards. It consists of an osseous and a cartilaginous portion, both 

 of which are covered with mucous membrane, which at the orifi- 

 cium pharyngeum is thicker than in the remaining parts, and at 

 the orificium tympanicum passes over into that of the tympanum. 

 Both openings (about two lines broad) are wider than the rest of 

 the canal (about one line broad). 



a. The osseous tuba, seven to eight lines long, is situated in the angle be- 

 tween pars mastoidea and petrosa of the Temporal bone external to canal, 

 caroticus, vestibule and cochlea, below the canalis tensoris tympani. To its 

 rough border is attached : 



b. The cartilagino-membranous tuba, the internal half of which consists of 

 cartilage, whilst the external wall is formed of a fibrous coat which is attached 

 to the Sphenoid bone. It lies above the fossa pterygoidea at the inferior bor- 

 der of the ala magna of the Sphenoid bone. Its oval opening (four lines high, 

 two broad) is tumefied, sloped, situated close behind and rather above the 

 inferior nasal concha, at the superior part of the pharynx. The mucous mem- 

 brane covering it is looser, very vascular, and beset with numerous mucous 

 glands which are wanting in the osseous tuba. Through the tuba the external 

 air obtains admission to the tympanum. 



Vessels and nerves for the central part of the organ of hearing. Arteries : 

 Artt. tympauica, stylomastoidea, farther branches from Art. meningea media, 

 pharyngea ascendens and carotis interna (for tuba Eustach.) 



Veins : they open into the plexus phary?igeus and meningea media. 



Nerves : they come from the fifth, seventh, and ninth cerebral nerves ; they 

 are : Chorda tympani ; passes from Canalis Fallopice in a canal peculiar to 

 itself, then into the tympanum (between manubr. mallei andproc. long, incudis), 

 and out through ihejissura Glaseri to ram. lingualis of the nerv. trigeminus ; 

 it gives off no branches in the tympanum. Anastomosis Jacobsonii gives two 

 filaments to the membrane in the region of ihefenestra, and one filament to the 

 tuba (where by pressure of the vessels in sanguineous congestion violent pain 

 arises). 



C. The internal part, the Labyrinth. 



512. 1. The osseous labyrinth, labyrinthus osseus. 



1. The vestibule, vestibulum, a small oval cavity (three lines 

 high, two broad, and one and a half deep) in the centre of the la- 

 byrinth, behind the Cochlea, before the semicircular canals, situ- 

 ated in the direction of the long axis of meatits auditorius inter- 

 nus, abutting externally on the tympanum, above, on the Canal. 

 Fallopice, below, on i\& foramen jugular e. We see in it 



a. Seven larger openings : 



