chap, v.i THE EAK. 81 



long, and by opening into the pharynx serves to keep 

 a proper supply of air in the tympanum, and so 

 equalise the pressure upon the two sides of the mem- 

 brane. The floor of the tympanum is below the level 

 of the floor of the Eustachian tube. The line of 

 direction of the tube lies almost exactly midway be- 

 tween the transverse and antero-posterior axes of the 

 base of the skull. In the adult it inclines downwards, 

 so as to form an angle of 40 with the horizon. In the 

 child this angle is only 10" (Symington). In adults 

 |ths of the tube is cartilaginous and th bony (Syming- 

 ton). On the outer side of the tube lie the tensor 

 palati, the third division of the fifth nerve and the 

 middle meningeal artery. On the inner side are the 

 retro-pharyngeal tissue and (quite posteriorly) the 

 internal carotid artery. The pharyngeal orifice of the 

 tube is usually shut. During swallowing, however, it 

 is opened, by the action mainly of the tensor palati 

 muscle. If the nose and mouth be closed, and the 

 cheeks blown out, a sense of pressure is produced in 

 both ears. The hearing, at the same time, is dulled, 

 and the change is due to the bulging out of the mem- 

 brana tympani by the air thus forced into the tym- 

 panum. This method of inflating the middle ear is 

 known as Valsalva's method. 



In " Politzer's method " of passing air into the 

 Eustachian tube, the patient's mouth is closed, while 

 into one nostril the nozzle of a caoutchouc bag filled 

 with air is introduced, and the nostrils then held 

 firmly closed. The patient is asked to swallow a 

 mouthful of water, while at the same moment the bag 

 is forcibly emptied, and the air, having no other means 

 for escape, is thus driven into the open Eustachian 

 tube. The surgeon listens for the little noise caused 

 by the entrance of the air by means of a tube that 

 passes between the patient's meatus and his own. Pro- 

 longed closure of the Eustachian tube leads to deafness, 



G 4 



