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THE POPULAK EDUCATOR 



nected with sound is unexplained, because there are so many 

 structures connected with the organ which has been given us as 

 the recipient and interpreter of sound, at the use of which we 

 can hardly guess. 



That which is usually called the ear is familiar to every one 

 as the external semi-circular cartilage, closely invested with 

 skin, and ending below in a soft lobule, which is sometimes the 

 support of barbarous pendants. This structure, which, when 

 well formed, has a beauty of its own that needs no supplement 

 or advertisement, is but a remote appendage to the true ear. 

 Though it in some sort collects sound, and protects the orifice 

 which leads down towards, not to the true ear, it is non-essential, 

 and can be dispensed with without much inconvenience : so 

 that some of our poor ancestors, who found that they could not 

 retain both good external ears and good consciences, like 

 William Prynne in the time of Charles I. and the Star Chamber, 

 suffered less real loss than might have been anticipated. 



The external gristly ear is called the pinna, and though flat- 

 tened as to its general surface, is somewhat folded into ridges 

 and furrows, there being a rim round the outside and a channel 

 within this, which deepens and widens as it runs first upward, 

 along the back part, then downward along the fore part to a 

 central crypt. From this crypt the passage becomes narrower 

 as it runs forward and inward to the pit of the ear. Sound, no 

 doubt, is conveyed along this canal in the same direction as we 

 have described its course. If the pinna were quite flat, sound 

 would rebound from it ; but as it is so shaped, sound is caught 

 and reflected round the canal from point to point, as it is reflected 

 round the Whispering Gallery of St. Paul's, and finally delivered 

 down the tube of the ear. 



The tube is an inch and a half deep, and its innermost half 

 enters one of the bones of the head, called the temporal bone, 

 and in this bone all the other parts of the ear are enclosed and 

 protected. At the bottom of the tube is an oval membrane 

 stretched across the passage, and barring the entrance to all 

 external objects. Behind this is a roundish, irregular cavity, 

 filled with air. This stretched fibrous membrane bounding the 

 air cavity, naturally suggests the idea of a drum, shaped like a 

 kettle-drum; and hence the cavity is called the tympanum, from 

 a Latin word meaning drum, and the parchment-like tissue the 

 membrane of the drum. It differs, however, from a kettle-drum 

 in that several orifices open into it, and it contains structures to 

 be described presently. 



On the further side of the drum is the true ear. completely 

 encased in bone, except at two very small holes, which are closed 

 with membrane. The larger and upper aperture is called the 

 oval hole, and the smaller and lower the round hole. From the 

 membrane of the tympanum to the membrane of the oval hole 

 stretches a chain of bones, whose shape is best seen in the en- 

 graving. The outer one, next the parchment of the drum, is 

 called the hammer. It has three processes, or projections, two 

 of which are long ; so that, rather than hammer, it might be 

 called a woodcutter's beetle. One of these processes, called the 

 handle, is attached to the centre of the membrane, which it 

 makes tight when pulled inward by a small muscle, and lax 

 when another muscle acts on it. 



The former operation is probably the action which we uncon- 

 sciously cause when we consciously listen. The head of the 

 hammer is applied to another bone called the anvil (incus). It 

 has two processes, one for its suspension to the wall of the 

 tympanic cavity, and the other to connect it with the third or 

 stirrup-bone (stapes). This bne is more like the article it is 

 named from than the others are, and the foot-part of the stirrup 

 is applied to the oval membrane, which it nearly covers. These 

 bones can move a little in relation to one another, and their 

 actions are limited by small muscles, but they usually act to- 

 gether as if in one piece, playing round an axis which runs 

 through the heads of the hammer and anvil, so that when the 

 tympanic membrane is thrust in and out by vibration, the mem- 

 brane of the oval hole is made to vibrate correspondingly. The 

 round hole is open to the influence of sound conveyed through 

 the air of the tympanum ; but whether this be its function, or 

 merely to allow the fluid of the internal ear to be more readily 

 thrown into vibration in the passage it fills in other words, 

 whether it be a hole for the entrance or exit of vibrations seems 

 hard to tell. 



The fore-part of the drum cavity is connected with the throat 

 by a passage, which runs forward and downwards to open in the 



gullet behind the nose and mouth. Through this passage the 

 cavity is kept supplied with renewed air at the tame pressure- 

 as the external air. The reader may be conscious of the existence 

 of these passages to the ears from the throat by preventing the 

 air from rushing out of the mouth and nose, while he forces it 

 up from his lungs. The cavity of the drum will then be dis- 

 tended with air ; hearing will be less perfect, by the unnatural 

 tension of the membranes, and there is a slight singing in the 

 ear. With a little practice, air may be conveyed through th& 

 mouth to the drum, without entering the lungs, and thus gases 

 have been applied as remedies to diseases of the car. But the 

 exclusion of these from the lungs is difficult, and cannot be relied 

 on. One of our greatest aurists, when pursuing his philan- 

 thropic and scientific investigations on the effect of chloroform 

 and prussic acid applied thus, died, because he could not exclude 

 the latter deadly poison from his lungs as he had supposed he 

 could. The proper, or essential ear, consists of a chamber longer 

 than broad, communicating on its upper and outer side with 

 three semi-circular canals, and at its front inner end with a 

 cavity shaped like a snail-shell. 



*The chamber is called the vestibule ; this and the semi-cir- 

 cular canals are called together the labyrinth; and the hollow, 

 like that of a snail-shell, the cochlea. They are all channelled 

 out of the substance of the skull-bone before named as the tem- 

 poral. The part of this bone which lodges them juts inwards, 

 so as to lie at the base of the brain, and is so strong and thick 

 as to be called the petrous or stony part of the bone. Accurately 

 resembling the bony labyrinth in shape, but a little smaller in 

 its dimensions, so as to allow a little liquid to lie between it 

 and the bone, is a membranous labyrinth. That part of the 

 membrane which is on the floor of the vestibule leaves its 

 proximity to the bone at the entrance of the cochlea, and forms 

 a horizontal stage across the widest part of the spiral passage, 

 and so mounts round the three whorls of the spire, dividing it 

 into two parts ; so that, if we may imagine a small insect ex- 

 ploring these regions, it could mount to the apex of the spire 

 by either of two spiral staircases, the roof of the lower one being 

 the floor of the upper. These circular staircases only commu- 

 nicate with one another at the point of the shell. The lower 

 one at its foot communicates with the tympanum by the round 

 hole, while the vestibule communicates with the chain of bones 

 by the oval hole. Hence, if our imaginary insect could gain 

 access to the cochlea through the membrane of the round hole, 

 it must first mount to the top of the lower staircase, and then 

 descend all the way down the upper one, before it could explore 

 the labyrinth. 



All the cavities are filled with fluid, by whose agency the 

 vibrations are conveyed along its walls ; and in these walls, 

 especially at certain parts, are distributed the nerve-fibres of 

 the nerve of hearing. It would seem, however, as though the 

 vibrations of the liquid are not enough to impress the nerve, 

 and there are found small, hard structures wherever the nerve- 

 threads are most thickly placed, and at two places in the floor 

 of the vestibule are found collections of small, hard, marble 

 stones, held in a mesh of fibres ; so that, as the waves sweep- 

 by in the liquid, these are made to strike and rebound against 

 the nerves. The spiral sheet of membrane which divides the 

 cochlea receives the nerves from a main nerve which runs up 

 the central pillar, and it has in its substance fibrous bars, which 

 radiate outwards at regular intervals, like the key-notes of a 

 piano, and, like these, each is supposed to receive and transmit 

 to the nerve at its root a separate note. Thus the spiral sheet 

 of the cochlea is supposed to be able to appreciate difference in, 

 tone, and the labyrinth differences in the amount of sound. 

 The nerves from all parts are collected into one bundle, but, as 

 is usual with nerves wherever they may be found, the strands 

 remain distinct. 



To assist the reader in his conception of the ear, we may 

 compare it to a house of business. The pinna is the house-front ; 

 the tube is the porch ; the drum-membrane the front door 

 (closed) ; the drum is the hall : a few steps, the ossicles, lead 

 to an office, round which are convenient counters, closets, and 

 passages, at which clerks enter business transactions ; while, 

 directly communicating with this large office, cognisant of all 

 proceedings, but reserving to himself any special business, sits 

 the general manager, who has also a door direct to the hall ; 

 whilst, at the back of the premises, telegraph wires run to the 

 London agent. 



