1138 THE ORGANS OF SPECIAL SENSE 



middle ear. The Eustachian tube is accessible from the nose. If the nose and mouth be closed 

 and an attempt made to expire air, a sense of pressure with dulness of hearing is produced in 

 both ears, from the air finding its way up the Eustachian tube and bulging out the membrana 

 tympani. During the act of swallowing, the pharyngeal orifice of the tube, which is normally 

 closed, is opened, probably by the action of the Dilatator tubse muscle. This fact was employed 

 by Politzer in devising an easy method of inflating the tube. The nozzle of a rubber syringe is 

 inserted into the nostril; the patient takes a mouthful of water and holds it in his mouth, both 

 nostrils are closed with the finger and thumb to prevent the escape of air, and the patient is fhen 

 requested to swallow; as he does so the surgeon squeezes the bulb and the air is forced out of the 

 syringe into the nose, and is driven into the Eustachian tube, which is now open. The impact 

 of the air against the membrana tympani can be heard by the surgeon, if the membrane is intact, 

 sound being conveyed by means of a piece of rubber tubing, one end of which is inserted into 

 the meatus of the patient's ear, the other into that of the surgeon. The direct examination of 

 the Eustachian tube is made by the Eustachian catheter. This is passed along the floor of the 

 nostril, close to the septum, with the point touching the floor, to the posterior wall of the pharynx. 

 When this is felt, the catheter is to be withdrawn about half an inch, and the point rotated out- 

 ward through a quarter of a circle, and pushed again slightly backward, when it will enter the 

 orifice of the tube, and will be found to be caught, and air forced into the catheter will be heard 

 impinging on the tympanic membrane if the ears of the patient and surgeon are connected by a 

 rubber tube. 



THE INTERNAL EAR, OR LABYRINTH (AURIS INTERN A). 



The internal ear is the essential part of the organ of hearing, receiving the 

 ultimate distribution of the auditory nerve. It is called the labyrinth, from the 

 complexity of its shape, and consists of two parts, the osseous labyrinth, a series 

 of cavities channelled out of the substance of the petrous bone, and the membranous 

 labyrinth, the latter being contained within the former. . 



Opening of aqueductus vestibuli. 

 Bristle passed through foramen rotundum. 



Opening of aqueductus cochlese. 



FIG. 846. The osseous labyrinth laid open (enlarged). 



The Osseous Labyrinth (labyrinthus osseus) (Fig. 846) consists of three parts 

 the vestibule, semicircular canals, and cochlea. These are cavities hollowed out 

 of the substance of the bpne, and lined by periosteum. A clear fluid is contained 

 in the space between the osseous labyrinth and the membranous labyrinth. The 

 space is called the perilymph space, and the fluid is called perilymph. 



The Vestibule (vestibulum) (Figs. 840 and 846) is the common central cavity 

 of communication between the parts of the internal ear. It is situated on the inner 

 side of the tympanum, behind the cochlea, and in front of the semicircular canal? 



