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Lastly-like the other senses, smell is capable of great improvement by education. The perfumer arrives, by habit, at an accurate discrimination of the nicest shades of odours; and the chemist and the apothecary employ it to aid them in distinguishing bodies from each other; and in pointing out the changes that take place in them, under the influence of heat, light, moisture, &c. In this way, it becomes a useful chemical test. The effect of education is likewise shown, by the difference between a dog kept regularly accustomed to the chase, and one that has not been trained. For the same reason, in man, the sense. is more exquisite in the savage than in the civilized state. In the latter, he can have recourse to a variety of means for discriminating the properties of bodies; and hence has less occasion for acuteness of smell than in the former; whilst, again, in the latter state, numbers destroy the sense to procure pleasure. The use of snuff is one of the most common of these destructive influences.

Of the acuteness of the sense of smell in the savage we have an example on the authority of Humboldt: he affirms, that the Peruvian Indians in the middle of the night can distinguish the different races by their smell,-whether they are European, American, Indian, or negro. To the same cause must be ascribed the delicacy of olfaction generally observed in the blind.. The boy Mitchell,' who was born blind and deaf, and whose case will have to be referred to hereafter, was able to distinguish the entrance of a stranger into the room by smell alone. A gentleman, blind from birth, from some unaccountable impression of dread or antipathy, could never endure the presence of a cat in the apartment. One day, in company, he suddenly leaped up; got upon an elevated seat; and exclaimed, that a cat was in the room, begging them to remove it. It was in vain that the company, after careful inspection, assured him he was under an illusion. He persisted in his assertion and state of agitation; when, on opening the door of a small closet, it was found that a cat had been accidentally shut up in it.

SENSE OF HEARING OR AUDITION.

Audition makes known to us the peculiar vibrations of sonorous bodies, that constitute sounds. It differs from the senses which have already been described, in the fact, that contact is not required between the organ of sense and the sonorous body; or between it and any emanation from the body. It is, however, a variety of touch, but produced by a medium acted upon by the vibratory body.

1. ANATOMY OF THE ORGAN OF HEARING.

The auditory apparatus is a subject of intricate study to the young anatomist; and unfortunately when he has become acquainted with the numerous minute portions to which distinct and difficult appellations. have been appropriated, he has, as in many other cases, attained a tedious detail of names, without having added to his stock of physio

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Wardrop's History of James Mitchell, Lond., 1813; and Dugald Stewart's Elements of the Philosophy of the Human Mind, iii. 401, 3d edit., Lond., 1808.

logical information. Happily, it is not necessary for our purpose to go so minutely into the description of the organ of hearing. According to the plan hitherto pursued, allusion will be made to those portions only that concern the physiological inquirer.

In the ear, as well as in the eye, we have the distinction between the physical and nervous portions of the organ more clearly exhibited than in the skin, mouth, or nose. The nervous portion is situate deeply within the organ; and the parts between it and the exterior act physically-on sonorous vibrations, in the case of the ear; and on light, in that of the eye.

Fig. 63.

[graphic]

State.

1, 2. Origin and termination of the helix. 3. Anthelix. 4. Antitragus. 5.

Tragus. 6 Lobus of the external ear.

7. Points to the scapha, and is on the 9. Meatus auditorius externus.

front and top of the pinna. 8. Concha.

The organs of the senses hitherto considered are symmetrical. Those of audi- View of the Left Ear in its Natural tion are two in number, distinct but harmonious, and situate at the sides of the head, in a part of the temporal bone, generally called, from its hardness, pars petrosa, and by the French and German anatomists regarded as a distinct bone, under similar appellations Le Rocher, and

Felsenbein, ("rock

bone.") This bone is

seated at the base of two d

the skull, so that the

internal parts of the auditory organ are deeply and securely lodged.

For facility of description, the ear may be divided into three portions:-1. External ear or that exterior to the membrana

Fig. 64.

[graphic]

tympani; 2. Middle General View of the External, Middle, and Internal Ear, as seen

in a Prepared Section. (From Scarpa.)

a. The auditory canal. b. The tympanum or middle ear.

c. Eus

tachian tube, leading to the pharynx. d. Cochlea; and e. Semicircular canals and vestibule, seen on their exterior, as brought into view by dissecting away the surrounding petrous bone. The styloid process projects below; and the inner surface of the carotid canal is

ear the space con-
tained between the
membrana tympani
and internal ear; and
3. The internal ear
in which the auditory nerve is distributed.

seen above the Eustachian tube.

1. External Ear. This portion of the auditory apparatus is com

monly looked upon as an acoustic instrument, for collecting the sonorous rays or vibrations, and directing them, in a concentrated state, to the parts within. It is composed of the pavilion, and meatus audi

torius externus.

The pavilion varies in size and position in different individuals. It is the fibro-cartilaginous, thin, expanded portion, which is an appendage, as it were, to the head. It is irregular on its anterior surface; presenting several eminences and depressions. The eminences are five in number; and have been called, by anatomists, helix, anthelix, tragus, antitragus, and lobe. The helix forms the rim of the pavilion: the tragus is the small nipple-like projection on the facial side of the meatus auditorius; the antitragus is the projection opposite to this,forming the lower portion of the anthelix; and the lobule is the fatty, pendulous portion, to which ear-rings are attached. The depressions are three in number-the groove of the helix or cavitas innominata; the fossa navicularis or scapha; and the concha. The name of the first sufficiently indicates its situation; the second is nearer the meatus auditorius; and the third is the expanded portion, which joins the commencement of the meatus, and is bounded by the anthelix, tragus, and antitragus. The pavilion is supple and elastic; and, beneath the skin are numerous sebaceous follicles, which are distinctly perceptible, and give the skin its polish, and probably a portion of its suppleness. On the different eminences, some muscular fibres are perceptible, which it is not necessary, for our purpose, to distinguish; for in man at least they are but vestiges-as the French term them-to indicate the uniform plan that appears to have prevailed in the formation of vertebrated animals: if they have any office it must be unimportant. Nu

Fig. 65.

Anterior View of the External Ear, as well as of the Meatus Audito

rius, Labyrinth, &c.

1. The opening into the ear at the bottom of the concha. 2. Meatus auditorius externus or cartilaginous ca

merous vascular and nervous ramifications are distributed on the pavilion. It is attached to the head by different ligaments, called from their situation or attachments -zygomato-auricular or anterior-auricular:-temporo-auricular or superior-auricular, and mastoido-auricular or posterior-auricular; all of which terminate on the convex part of the concha. Three muscles, in animals at least, are attached to the ear to move the pavilion. These occupy the same position as the ligaments described; and have similar names. In man, they, again, are mere vestiges; but in many animals-as the horse-they are largely developed, and capable of moving the pavilion in various directions; and there are persons, who possess a degree of voluntary power over it.

The meatus auditorius externus extends nal. 3. Membrana tympani stretched from the inner extremity of the concha to upon its ring. 4. Malleus. 5. Stapes. the membrana tympani. In the adult, it

[graphic]

6. Labyrinth.

is about an inch long; narrower in its middle than extremities; longer inferiorly than superiorly, owing to the obliquity of the membrana tympani; and slightly curved upwards about its middle. The outer orifice is furnished with down or hairs-vibrissæ-like the orifices of certain other canals. The meatus is osseous, for the space of half an inch, and penetrates the temporal bone. More externally, it is formed of fibro-cartilage,-a prolongation of that of the concha. It is lined by an extension of the skin, which becomes gradually thinner as it proceeds inwards, and is ultimately reflected over the outer surface of the membrana tympani. Beneath this skin, numerous sebaceous glands or follicles are situate, which secrete the bitter humour, called cerumen. This humour occasionally becomes inspissated; obstructs the canal; prevents sonorous vibrations from reaching the membrana tympani, and is thus the cause of deafness. Softening it, by means of warm water or oil, or soap and water dropped into the meatus, and removing it by means of the syringe, restores the hearing.

[graphic]

and its centre affords attachment to one extremity of the chain of small bones, to the handle of the malleus. The proper tissue of the membrane is dry, and it is generally esteemed to be devoid of fibres, vessels, and nerves. Sir Everard Home,' however, asserts, that it is muscular; that its fibres run from the circumference towards the centre, and are attached to the malleus; and that if the membrane of the human ear be completely exposed on both sides by removing the contiguous parts, the cuticular covering be washed off from its external surface, and it be placed in a clear light, the radiated direction of its fibres may be easily detected. This fibrous arrangement, Sir Everard conceives to be muscular, and on this he founds some ingenious speculations, to be hereafter noticed, regarding the appreciation of sounds. The discovery of a fibrous structure would, however, by no means prove, that the membrane is capable of contracting; or that it is formed of muscular tissue. Many ligaments, which consist of gelatin, and are, consequently, not contractile like muscles, are distinctly fibrous in their arrangement. The same may be said of tendons, whose utility, as conductors of force developed by muscle, would be materially interfered with, were they possessed of contractility. Again:Messrs. Ruysch, Sir Everard Home, and Sir Charles Bell, affirm, that the membrana tympani is vascular,-Sir Everard asserting, that the vessels, in their distribution, resemble those of the iris, and are nearly half as numerous;-their general direction being from the circumference to the handle of the malleus. It is not easy to account

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Fig. 67.

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for this discrepancy amongst practical anatomists as to the structure of the membrana tympani. A part of it is probably referable to some having directed their attention to the membrane proper; and others to the se membrane with its dermoid coverings, which are highly vascular.

and seen from the outside and below.

The inner extremity of the drum is partly osseous, partly membranous. Nearly opposite the centre of the membrana tympani is the foramen ovale seu vestibulare, called, also, the fenestra ovalis seu vestibularis, situate vertically, and forming a comOssicles of the left Ear articulated, munication between the middle and internal ear. It is closed by a membrane-consistm Head of the malleus below ing, like the membrana tympani, of three which is the constriction, or neck. ; layers-to which is attached the base of the Processus gracilis, or long process, at the root of which is the short process. stapes, the inner extremity of the chain of crus; and le, long crus of the incus. ossides that stretches across the cavity. The body of this bone is seen articu- Immediately below the foramen ovale is the crus, through the medium of the orbi bony projection called the promontory; and a, with the stapes. s. Base of the beneath this, again, a second opening, called foramen rotundum seu cochleare, and fenes

h. Manubrium, or handle. sc. Short

lating with the malleus, and its long

cular process, here partly concealed,

stapes.-Magnified three diameters. (From Arnold.)

Philos. Transact. for 1800, P. i. p. 1, and Lectures on Comp. Anat., iii. 262, Lond., 1823. 'Epist. Anat. octava, p. 10. Amstel., 1724.

3 Anat. and Physiol., edited by J. D. Godman, 5th Amer. edit., ii. 253, New York, 1827.

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