MIDDLE EAR. 36*7 



outer wall is composed partly of cartilage and partly of 

 fibrous tissue, covered by the tensor palati muscle. This 

 tube, where it opens into the pharynx, is thick, and pre- 

 sents a division into two angles, the anterior being con- 

 nected by fibrous tissue to the root of the internal ptery- 

 goid plate ; the posterior thick, prominent, and admitting 

 of motion. Its mucous tissue forms the internal lining, 

 and is continuous with that of the pharynx, and also with 

 that of the tympanum.* 



Function. To give passage to the air into the tympanum, 

 and to conduct the secretions from the tympanum to the 

 fauces. Obstructions in this tube, from inflammation and 

 other causes, are frequent sources of deafness. Above the 

 Eustachian tube, and separated by a thin osseous plate, is a 

 canal for the attachment of the tensor tympani muscle. 



The posterior wall, at its upper part, has an opening lead- 

 ing into the mastoid cells, which, like the tympanum, are 

 found to contain air, and are lined with mucous membrane. 

 Beneath this mastoid orifice is a small opening from the 

 aqueduct of Fallopius, transmitting the chorda tympani 

 nerve. 



The superior wall presents a depression for the head of 

 the malleus, and the body and short leg of the incus, It is 

 spongy, and has some small vessels passing through it to 

 the dura mater. 



The inferior wall is rough and narrow, formed by the 

 auditory and vaginal processes. It has a small opening 

 which gives exit to the chorda tympani nerve from the 

 cavity of the tympanum. 



The tympanum contains a chain of little bones, the 



* Muscles of Eustachian Tube. Joseph Toynbee, F. R. S., believes he has de- 

 monstrated that the mouth of the Eustachian tube is always closed, except 

 during deglutition; and that the cavity of the tympanum is always " distinct 

 and isolated from the outer air," except in deglutition. The muscles which 

 open this tube, he says, are the tensor and levator palati; and he further states 

 that the function of hearing is best carried on when the tympanum is closed, 

 entirely upsetting the opinion that the air within the tympanum must commu- 

 nicate with the outer air in the pharynx, that vibration may take place, and 

 hearing be produced. 2mer. Jour. Medical Science, Jlpril JVb., 1853. 



