Tnternal Ear 101 



been brought forward enough, but is lodged in the space between the 

 posterior part of the opening and the back of the pharynx the fossa 

 of Rosenmiiller. 



The catheter being securely inserted into the tube, the surgeon 

 connects his own ear with that of the patient by a flexible stethoscope 

 and listens for the result of pumping air along the catheter. If the 

 obstruction be absolute no air is heard rushing into the tympanum ; 

 if the tube be abnormally dry the sound is harsh, and if the tube and 

 the tympanum contain mucus the air enters with a bubbling. But, if 

 the obstruction be suddenly overcome, the air enters with a rush, driv- 

 ing the membrane outwards with a slight click. If the membrane be 

 perforated the air escapes with a hissing sound. 



If the catheter be so clumsily introduced as to tear the mucous 

 membrane, and if air be then pumped up with considerable force, tem- 

 porary emphysema of that neighbourhood may result. 



The internal ear is a labyrinthine chamber hollowed out in the 

 petrous bone, and consisting of three parts, the vestibule, semicircular 

 canals, and the cochlea, which have a delicate lining for the secretion 

 of perilymph. The bony labyrinth contains a membranous labyrinth of 

 corresponding shape ; it is hollow and floats in the perilymph ; it, like- 

 wise, contains fluid, the endolymph. Thus, the auditory filaments, which 

 are spread out upon it, are securely placed between the peri- and the 

 endo-lymph. The membranous labyrinth is supplied by a small audi- 

 tory branch of the basilar artery, which enters by the internal auditory 

 meatus. 



The semicircular canals occupy suggestive geometrical positions : 

 the superior is in a vertical transverse plane ; the posterior in a vertical 

 antero-posterior plane ; and the external one arches outwards in a 

 horizontal plane. Their function is probably for maintaining the equi- 

 librium of the head and of the body ; when they are diseased the 

 subject cannot keep upright. 



When the amount of fluid in the labyrinth is excessive the patient 

 has sudden attacks of giddiness, headache, and sickness, and he 

 promptly falls in a definite direction. He may at first think that the 

 associated troubles, which are accompanied by deafness, are due to in- 

 digestion. The disease is named after M. Meniere, who first described 

 it, and, because of its associations, it is often spoken of as ' ear 

 vertigo. 3 



The auditory nerve passes down the internal auditory meatus and 

 breaks up into branches which run through small holes to the vestibule, 

 semicircular canals, and cochlea. 



The waves of sound reach these terminal filaments by the mem- 

 brana tympani setting the ossicles in vibration, the oval plate of the 

 stapes imparting a similar movement to the perilymph, by which the 

 acoustic filaments are irritated. The nerve-filaments may also be set 

 in vibration by the conduction of sound through the bones of the skull. 



