HEARING. 257 



within. Its fibrous part is attached to the bone round about, 

 and has its principal fibres radiating from the lower end of 

 a process of an ossicle in the tympanum, the handle of the 

 malleus, which descends between the fibrous and mucous 

 layers. The membrane is sloped so as to approach nearer 

 the surface at its upper than its lower edge; and it is slightly 

 concave on its outer side, being pulled inwards at the point 

 where the malleus is attached. 



190. The middle ear, called also the cavity of the tympanum 

 or drum, is a space of greater vertical height than the canal, 

 and still more extensive from before backwards, but narrow 

 transversely. At its fore part is the opening into the Eusia- 

 chian tube, a passage about an inch and a half long, leading 

 into the pharynx (p. 89). This tube is small and bounded 

 with bone for a short distance at its tympanic extremity; 

 but in the rest of its extent is cartilaginous, and gradually 

 widens. Its cartilaginous wall is replaced with membrane 

 at its lower part, and is so related to the levator palati muscle 

 that, in the act of swallowing, that muscle momentarily 

 closes its pharyngeal extremity. It is lined with ciliated 

 epithelium, as is also the tympanum. It allows the passage 

 of air into the tympanum, but is very easily blocked up by 

 the adhesion of its walls, near its fore part; and if, when 

 this occurs, the tympanum have either too much or too little 

 air in it, the effect is a disagreeable sensation and interfer- 

 ence with hearing, liable to occur after violently blowing the 

 nose, and producible by holding the nostrils, and making a 

 strong expiration with the mouth shut, so as to force air into 

 the tympanum. When the sensation is produced, it lasts 

 for a variable length of time, according to the extent of 

 contact of the walls of the Eustachian orifice, and the 

 viscidity of the substance which causes them to cohere; and 

 it is often removed by the instinctive repetition of the act 

 of swallowing, and stretching the neck on the affected side, 

 so as to make a greater pull on the floor of the orifice, as 

 the parts fall back into their places on the cessation of the 

 spasm of deglutition,* 



* It is only fair to state that the opinion held by the late Mr. 

 Toynbee, that the Eustachian tube is in ordinary circumstances shut, 

 and is momentarily opened in swallowing, is held by many, both in 

 H 3 



