

EAR 



2759 



THE EAR: ITS ORGANISM & FUNCTIONS 



T. S. A. Orr, M.D., Aural Surgeon, Westminster Dispensary 



The Ear, Deafness, and Deaf and Dumb, with shorter entries, e.g. 

 Cochlea, form a group of related articles, another such group being 

 those on the Eye, Blindness, etc. See also Anatomy ; Man ; Surgery 



The ear is the organ of hearing, 

 more strictly the end organ of the 

 eighth cranial nerve. It has two 

 functions: it collects and concen- 

 trates the vibrations of air known 

 as sound waves and transmits them 

 to the nerve in order that they may 

 be perceived and interpreted in the 

 brain; and it harbours the chief 

 organ of balance or equilibration. 



The ear is divided into three 

 parts : ( 1 ) The outer ear composed 

 of (a) the auricle, or pinna, applied 

 to the side of the head, concave on 

 its outer aspect, and leading into 

 (6) the external auditory meatus, a 

 narrow tube passing inwards to the 

 drum of the ear. The outer ear is 

 composed chiefly of a framework of 

 cartilage covered by skin. The skin 

 contains hair only in the male, but 

 in both sexes it has sweat glands. 

 Wax in the ear, due to dried sweat 

 accumulating in the meatus, often 

 causes sudden and severe deafness 

 and can be seen as a dark plug well 

 down the meatus. In man the pin- 

 na is small and of little importance. 



(2) The middle ear is a small cav- 

 ity in the side of the skull separated 

 from the outer ear by the ear drum. 

 It has a chain of minute bones, the 

 hammer, anvil, and stirrup bones, 

 which run across it and carry sound 

 waves from the drum to the oval 

 window, a small hole, closed by a 

 membrane and leading into the 

 inner ear 



Relation of Throat and Ear 

 The cavity in addition transmits 

 the nerve of expression, the facial, 

 and an important nerve of taste, 

 the chorda tympani. It has in 

 front a tube that connects it with 

 the throat, the Eustachian tube, 

 and behind and above it communi- 

 cates with the air cells in the mas- 

 toid process, the projection of bone 

 seen behind the auricle. Inflam- 

 matory processes starting in the 

 throat may, therefore, pass up 

 through the middle ear to the mas- 

 toid process. As this is in very close 

 relationship to the brain, the dan- 

 ger of all middle ear inflammation 

 is apparent. In health the Eus- 

 tachian tube allows air to pass into 

 the middle ear in order that the 

 pressure of air inside the drum may 

 equalise the atmosphere pressure. 



(3) The inner ear is a cavity em- 

 bedded in the skull deeper than the 

 middle ear, and communicates with 

 it through the oval window, a mem- 

 brane like the drum of the ear in- 

 tervening. It is filled with fluid, 

 called perilymph, submerged in 

 which are two hollow structures 



composed of membrane the coch- 

 lea and the semicircular canals. 

 These again are filled with fluid, 

 called endolymph. The cochlea is a 

 spiral tube, and has been compared 

 to a snail-shell. The nerve of hear- 

 ing terminates in it, in a multitude 

 of minute hairs, which float in the 

 endolymph. Sound waves are car- 

 ried through the outer and middle 

 ear and put the membrane closing 

 the oval window in motion, which is 

 communicated to the fluid filling 

 the inner ear. The movement in this 

 fluid is communicated through the 

 membrane composing the cochlea 

 to the fluid contained therein, in 

 which the termination of the nerve 

 of hearing floats, the stimulus thus 

 given to the nerve being perceived 

 in the brain as sound. 



^ EAR 



The semicircular canals are three 

 tubes, at right angles to one an- 

 other, semicircular in shape, and 

 joined together. Like the cochlea 

 they are filled with fluid, having 

 fine hair-like nerve terminals float- 

 ing in it. Any movement of this 

 fluid stimulates the nerve. The fluid 

 is set in motion by any change in 

 the position of the body. The stimu- 

 lus so produced is carried to the 

 brain and enables it to judge of our 

 position in space and automatically 

 to adjust our muscles accordingly. 



FUNCTIONS OF THE EAR. The 

 cochlea is the only part of the inner 

 ear concerned in hearing. It is ab- 

 sent in fishes ; first appears in am- 

 phibia and reptiles, increases in 

 birds and attains its maximum per- 

 fection in mammals. The semicir- 

 cular canals, on the other hand, are 

 entirely concerned in the balance 

 of the body. They can be extir- 

 pated in birds and mammals with- 

 out causing any perceptible depre- 

 ciation of hearing ; destruction of 



Ear. 



Sectional diagram showing the construction and delicate mechanism 

 of the ear 



