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synonyme, agallochee, is also given, and more especially | (Enc. Méth., 1., p. 49, Illustr. t. 376.) The plant he named applied to aod-i-kimaree, which is also called aod-i-bukhoor, Aquilaria Malaccensis. This, the Garo de Malacca, was incense-wood. As agallochee is no doubt a corruption of introduced by Dr. Roxburgh into the Botanic Garden of the agallochum of Dioscorides, described by him as a fragrant wood from India and Arabia, it is interesting to find that the translators from the Greek into the Arabic of the school of Bagdad settled these synonyms at a time when they must have been well acquainted, from their profession and position, with the substances to which both the Greek and Arabic names were applied. Serapion and Avicenna describe several kinds of this fragrant wood, and the latter under both agalugen or aghaloojee, and aod, which in the Latin version is translated Xyloaloe, a name that was applied by the later Greek medical writers to agallochum, whence we have lignum aloes, lign-aloe, and aloes-wood, the origin of which it is difficult, if not impossible, to ascertain, unless we suppose it to be a corruption of agila; for the bitter, scentless, spongy-textured stems of the genus aloe could not afford any substitute for this fragrant wood, or be thought to yield it, at least by the Arabs, who were well acquainted with, and accurately describe aloes, and the place, Socotra, where the best kind is found. Though Dioscorides notices only one, which some supposed to be the Tarum of Pliny, several kinds of agallochum are described by Serapion and Avicenna, which, as it is not possible at present to identify, it is unnecessary to notice, and therefore we shall refer only to the three kinds which have been traced to the trees yielding them, by naturalists who have visited the countries where these are indigenous.

An Aguila brava (wild) is mentioned by Garcias as produced near Cape Comorin, in the southern part of the Indian peninsula, and in the island of Ceylon; but the tree yielding this wood has not been ascertained. Rumphius (Herb. Amb. ii. p. 40), describes two kinds of agallochum spurium, found in Borneo and Sumatra, one of which he calls Garo Tsjampaca, which is described as having leaves and flowers resembling those of the celebrated champa, Michelia champaca, and may be a species of the same genus. A third kind of spurious agallochum, differing much from the others as well as from the genuine, he describes in another part of his work, ii. p. 240, as the produce of his Arbor excæcans, so called from the acridity of its juice blinding people, and which is the Excæcaria agallocha of Linnæus. Considering that Rumphius, in originally describing this tree, has said 'Lignum hoc tantam cum agallocha similitudinem,' and as affording a substitute for that substance, it is not surprising that it should be frequently quoted as the tree which yields the genuine agallochum, or aloes-wood. Fée (Hist. Nat. Pharm.) states that he had seen a genuine specimen of the wood of this tree, and that its fragrance cannot be compared with the agallochum of Loureiro. Dr. Roxburgh mentions that the wood-cutters of the Delta of the Ganges, though well acquainted with the highly acrid and very dangerous milky juice of this tree (there called geria), do not mention agallochum of any kind being found in this tree.

Of the two kinds of agallochum which are most valued, and both considered genuine, one is distinguished by the name of Calambac, and the other as the Garo of Malacca.

The first, called calambac, and agallochum primarium by Rumphius, appears, as far as hitherto known, to be a native of Cochin China only, growing on the mountains of that country in about 13° of N. lat., near the great river Lavum, which may be the Meikeng flowing between Cochin China and the Laos. This tree was named Aloerylum agallochum by Loureiro, Fl. Cochin Chinensis, p. 327, and placed by him in Decandria Monogynia, and described as a lofty tree with erect stem and branches, long lanceolate shining leaves, terminal bunches of flowers, with a woody, falcate, one-seeded pod for its fruit, whence it is referred by De Candolle to the natural family of Leguminosa. Loureiro states that the wood of this tree is white and inodorous, and that its fragrance is the result of disease, when the oily portions thicken into resin in the central parts of the tree, and that no part of the tree is milky or poisonous, but that paper is made from its bark in Cochin China, as in Japan from that of the mulberry.

Calcutta, and was not to be distinguished from specimens of a tree called ugoon, which is a native of the mountainous tracts east and south-east from Silhet, between 24° and 25° of N. lat., which flowers in April, and ripens its seed in August, and which he says there can be little or no doubt furnishes the real Calambac or Agallochum of the antients; adding, that there seems more reason to think that it was carried to China from our eastern frontier, than to suppose it was carried from Cochin China, or any other country in the vicinity of China, where it has always been in great demand. Small quantities are sometimes imported into Calcutta by sea, from the eastward; but such is always deemed inferior to that of Silhet. (Fl. Ind. ii. p. 423.) As the Malacca plant had not flowered, Dr. Roxburgh was unable to decide that they were positively the same with those from Silhet, and therefore named these Aquilaria agallochu, as another species of the same genus. By this name it has been figured in Royle's Illustr. i. 36, f. 1, from a drawing by Dr. Hamilton of a plant which he called Agallochum officinarum, and which he found near Goalpara, on the eastern frontier of Bengal. This drawing is illustrated with dissections by Dr. Lindley. To the above-quoted work, and the latter's Natural System of Botany,' we refer for the botanical details and the characters of the family of Aquilariaceae, to which this genus gives its name. The fragrant nature of genuine agila or eagle-wood is well known, and that it has from very early periods been employed both by the natives of India and of China as incense. Mr. Finlayson, in his visit to Siam, says, that the consumption of this highly odoriferous wood is very considerable in Siam, but that the greatest part is exported to China. In the latter, it is used in a very economical manner; the wood being reduced to a fine powder and mixed with a gummy substance is laid over a small slip of wood, about the size of bull-rush, so as to form a pretty thick coating. This is lighted, and gives out a feeble but grateful perfume. French authors inform us that the eagle-wood was burned as a perfume by Napoleon in the imperial palace.

We cannot conclude this subject without inquiring whether the substances of which we have been treating are the lign-aloes of Scripture, ahaloth, masc. ahel, whose plural is ahalim. It would be impossible to do justice to the subject in a small compass, or without referring to the numerous dissertations which have been written on it; but it may be observed, that these might have been much shortened, if the authors had been naturalists, or intimately acquainted with the natural history and usages of eastern countries; such information would at least have prevented any species of aloe being considered or figured as the far-famed and fragrant lign-aloe from a mere similarity in sound. In the present instance, the difficulty is increased by the supposed necessity of reconciling the different passages in which lign-aloes are mentioned, as in Numbers, xxiv. 6, where it is mentioned as a tree planted; but in the three other passages, Prov. vii. 17, Psalms xiv. 9, and Canticles, iv. 14, it is enumerated with the most fragrant products of the East, as cinnamon, cassia, calamus, camphor, frankincense, myrrh, spikenard, and saffron. Here we may observe, that a substance which was indigenous in a country was not likely to have been an article also of commerce from a far country in those early times; and that therefore, as it is disputed whether the word shall be translated tents or lign-aloes, the word may perhaps be used in a poetical sense, as it is thought to be by some commentators. In the three passages, it may be noted, that, except sandal-wood, there is no other substance which could be so well enumerated with those with which it is found in connexion as the agila wood of the East, whether we consider its high price, delicate perfume, or the long time in which it has been held in high estimation, while the similarity of its name is at the same time remarkable. EAGRE. [BORE.]

EAR. Many animals unquestionably enjoy the faculty of hearing to a limited extent, which are found, upon exaThe next kind of agallochum is that commonly called mination, to be unprovided with organs exclusively approgaros, and to which the name of eagle-wood is more fre- priated to the concentration and transmission of sound. In quently applied, and which has long been an article of ex-fact, the sense of hearing is, strictly speaking, only a refineport from Malacca and the kingdom of Siam. Specimens of the tree which yield this were first obtained by M. Sonnerat in his second voyage to India, from which probably have been given the figure and description by Lamarck.

ment of the sense of touch. The impressions with which
it is conversant arise wholly [ACOUSTICS] from peculiar
undulations of the particles of ordinary matter, propagated
in obedience to its ordinary laws through the medium in

which the animal lives, and impinging more or less imme-tributed to the membranous bag just described is given ou diately upon a sensitive part; they have no necessary de- by that which supplies the antenna with its exquisite sense pendence, like those of sight, upon the agency of the more of touch: some have thought, but perhaps erroneously, subtle fluids; nor have they any connexion, like those of that the faculty of hearing resides in the antennæ themsinell and taste, with what may be called the chemical pro- selves. perties of matter. If to these considerations it be added that the vibratile substances which are commonly found to inclose the sensorium are not ill qualified to participate in the undulations of the surrounding medium, and carry them onwards to the internal seat of perception, the reader will be prepared to learn that the only essential part of the | organ of hearing is a nerve, not materially different from those of common sensation, lodged at a sufficient depth to be secured from external injury, and sufficiently sensitive to be affected by these delicate impulses. This is called the acoustic or auditory nerve.

The parts we have enumerated are all found, with others, in the higher animals, and may be considered as the most essential parts of an organ of distinct hearing. The cavity is called the vestibule; the soft membranous bag of fluid is the vestibular sac; the round external opening is called, from its shape in man and most other animals, the fenestra ovalis; the fluids within and without the sac are called respectively the endo-lymph and peri-lymph, (Evdov within, Tepi around); the latter, being analogous to the fluid discovered by Cotugno in the internal ear of mammalia, is sometimes called, after his name, the liquor Cotunni. The principal tribes of the Articulata ascertained to possess organs of this kind are the air-breathing insects of tne orders Hymenoptera (bees), Orthoptera (grasshoppers), and Coleoptera (beetles); the Arachnida (spiders), and the Decapodous crustacea, such as the lobster and crab. In the common black beetle they are very conspicuous, appearing externally in the form of round white points on the head, a little nearer the middle line, and somewhat higher than the base of the long outer antennæ. In the lobster they are contained in a small nipple-like prominence or papilla upon the under part of the moveable base of the antennæ, looking downwards and forwards. This papilla consists of a substance harder and more brittle and probably more vibratile than the rest of the shell.

It is probable that even the lowest animals provided with a nervous system are able to perceive the notices thus conveyed of external objects, and turn them to account in the degree necessary for their security and comfort. But to meet the increasing wants and minister to the multiplied faculties of the more complete animals, various subsidiary parts are found to be added in something like a regular succession as we advance upwards in the scale, each lower grade possessing the rudiments of some additional provision more fully developed in the next above, till the organ reaches its greatest amplification and final perfection in man and the other mammalia. The particular use of many of these subsidiary parts has not yet been explained. We know in general that they must increase the force and vividness of the impression; that they afford indications of its direction, and the means of appreciating minute shades of difference in its kind and degree, and in the frequency of its repetition; that some of them add to the security of the organ without impairing its delicacy; and that others serve to adjust its position and to adapt it to various changes in the state of the atmosphere. It would be superfluous, in a work addressed to the general reader, and limited in In the Sepia, or cuttle-fish, which belongs to this order, and space, to trace these gradual and complicated changes: we which may be taken as a type of the rest, there is a protubemust content ourselves with noticing some of the most im-rance under the elastic gristly integument at the back part portant of them, and then pass on to the description of the organ as it exists in man: advising the curious inquirer, after he has made himself acquainted with the details of that organ and with the classification of animals by Cuvier, an outline of which is given in a former part of this work [ANATOMY, COMPARATIVE], to consult the admirable essay on this subject by Professor Grant, in the third part of his 'Outlines of Comparative Anatomy,' where he will find a comprehensive and masterly summary of all that is known on the subject, from which we should be inclined to quote largely here, were space allowed and selection easy.

The Mollusca, though placed higher in the scale of animals by Cuvier, do not afford so many examples of animals possessing a distinct organ of hearing as the Articulata. Such as have been discovered all belong to the order of the Cephalopods with two branchia, or gills, which approach more nearly to the true fishes in their structure than the other mollusks.

The Radiata (star-fish, sponges, &c.), which constitute the lowest, and in point of variety and number by far the most comprehensive division of Cuvier, appear to be universally unprovided with an organ of hearing: many of them have no nervous system, and are therefore probably altogether devoid of the sense.

of the head which contains the ear. It consists of a pair of symmetrical vestibules, each containing an oval sac filled and surrounded with fluid. On the interior surface of this sac the acoustic nerve is expanded in the form of a white mucous pulp. The sac is supported in the perilymph not only by an adhesion to the inner side of the parietes of the vestibule at the entrance of the nerve, but also by a fine net-work of fibrils which pass from its outer surface to numerous prominent points on the inner surface of the vestibule. There is no fenestra ovalis, or membrane, as in the lobster and the air-breathing insects, but the sac contains a small loose bony or chalky concretion, called an otolithe (ovc-wròs, the ear, and Ai0os, a stone), which answers the same purpose, namely, to indicate the degree and direction of sound; for just as we estimate a weight by poising it in the hand, or, if it be suspended, by gently pushing it from us-thus measuring in our minds the muscular The Articulata, which form the next division, are all fur- tension necessary to support it, or the force required to nished with a nervous system, and it is likely that they all overcome its inertia, and conscious of the direction in which enjoy the sense of hearing. Indeed, some of them are able we exert our muscles-so, conversely (the weight and inertia to express their feelings and wants to their fellows by means of the lapillus always remaining the same), the degree and of peculiar sounds, of which the cricket and queen bee are direction of a vibratory force affecting it from without well-known examples. We find accordingly, that in many through the medium of the integuments, the parietes of the of the more perfect species the extremity of the acoustic vestibule, and the fluids within, may be estimated by a connerve is expanded upon a simple kind of auditory instru-sciousness on the part of the animal of the nature of the ment consisting of a whitish membranous bag of fluid, stress on the sensitive membranes and fibrils which supplaced within the head in a somewhat larger cavity, the port it, which by their elasticity restrain and redress the space between them being also occupied by fluid. This slight movements impressed upon it. This should be borne cavity is situated near the outer feelers, or antennæ. When in mind; for, as we shall see further on, it is in some the animal lives in water, it is commonly complete; if in degree by the exertion of the muscular sense, as Sir Charles air, there is a round external opening closed by a thin, Bell has called that by which we judge of weight and tense and transparent membrane, showing the white colour tension, that the human ear is enabled to estimate the inwithin, to which the bag adheres, and which receives, con- tensity of sound. Other curious particulars as to the funccentrates, and transmits the sonorous vibrations of the sur- tion of otolithes might be enlarged upon; but we have said rounding medium. This kind of arrangement seems to be enough to explain, as we think, the most important of necessary, among other reasons, for the purpose of indi- them; and to correct the misstatements of authors who cating the direction of the sound, which is probably made tell us that they are intended to increase the intensity of known in part by the clearer vibration of the membrane the vibrations of sound: they appear to us rather calculated when turned in that direction, and in part by a comparison to diminish it, as the board floating in the bucket of the of the impressions on the two sides; for this organ, like all water-carrier tends to prevent the fluid from dashing over others which bring the animal into relation with the outer the side. They undoubtedly play an important part in the world (as distinguished from vital organs), is always double organ of hearing, especially in the larger fishes, where and symmetrical. It may be observed that the nerve dis- they are more numerous, and attain a considerable size;

but it is difficult to conceive that they are possessed of any matter, and all the semicircular tubes communicate with a intensative power.

The vertebrated classes of the animal kingdom, comprising the true fish, reptiles, birds, and the mammalia, are all provided with acoustic organs, which are very various in their degrees of complexity, but much exceed in that respect the comparatively simple organs of the inferior divisions.

central membranous sinus, which the anterior and posterior tubes enter by a common trunk. The fenestra ovalis is closed, not as in fishes by a membrane, but by the expanded trumpet-shaped extremity of a slender bone (ossiculum or columella) attached at the other extremity by a ligament to the outer end of the intermaxillary bone.

* In the cartilaginous fishes, such as the ray and the snark, the vestibule is deeply imbedded in the elastic walls of the back part of the cranium, near its junction with the spine. The fenestra ovalis, closed by a tense transparent membrane, faces upwards, backwards, and towards the middle line. The membrane is placed obliquely at the bottom of a more superficial, flattened, tubular cavity, which terminates beneath the integument in a kind of forked ex-footed reptiles, permits the vestibule to be placed with equal tremity, and may be considered as a rudiment of the tymTanum, or middle ear, of the higher vertebrata, with its eustachian tube. The inner surface of the membrane is turned towards three sacculi, one of which is much larger than the rest, arranged at the opposite side of the cavity of the vestibule, and containing each an otolithe. The sacs are filled with a thick gelatinous endolymph, which adheres to the lapilli, and serves, with minute filaments such as those in the sepia, to steady them. The vestibule is filled with a limpid aqueous perilymph, traversed in all directions by a fine cellular network, by means of which its contents are supported in their relative situations. Besides the fenestra ovalis, other perforations lead out of the vestibule into three arched cylindrical canals of considerable diameter and dimensions, the diverging curves of which take a wide circuit within the cranial cartilage, and terminate at both ends in this central cavity. These passages, from their situation and form, are called the anterior, posterior, and horizontal semicircular canals. Within the canals, in which the vestibular perilymph freely circulates, there are three similarly curved but more slender membranous elastic tubes: they are nowhere in contact with the sides of the canals, but are suspended in the midst of them by means of the cellular network above mentioned. They all swell out at one end like a flask (ampulla) as they enter the vestibule, after which the anterior and horizontal tubes separately enter a common pouch or sinus; into this their other ends likewise open by a conduit common to both. The posterior tube, which is the largest and longest, after forming its ampulla, resumes its former calibre, and passing along the floor of the vestibule under the largest sac, to which it is connected by the net-work, returns into itself, thus completing a separate circuit.

The fluid contents of the several membranous cavities do not communicate with each other or with the vestibular perilymph; though, as they lie in close apposition, their vibrations are mutually interchangeable.

Nearly the same arrangement of the internal ear prevails in the four-footed reptiles (turtle, crocodile, frog, lizard); but a new and important step is here made towards the ultimate perfection of the organ by the development of an aircavity, called the tympanum or ear-drum, between the vestibule and the surface of the head. This addition, which, as we said, first becomes more than a mere rudiment in the fouradvantage at a comparatively greater depth, and therefore in greater security; but it has more important uses in rendering the sound more clear, and facilitating in several ways (to be presently explained) its communication to the auditory nerve. Like the musical instrument from which it takes its name, the tympanum is provided with a membrane tightly stretched upon the margin of a round opening in the outer part of its bony or cartilaginous wall; and has an open vent or passage called after the anatomist who discovered it, the Eustachian tube, leading forwards from the cavity to the throat or back part of the nostrils, by means of which the air within it is adjusted to the variable state of the atmospheric pressure without. If the animal be amphibious, as many of the four-footed reptiles are, the membrana tympani is still covered entirely by integument, sometimes, as in the crocodile, by a movable flap of the scaly hard skin, which can be raised up when the animal is out of the water: more frequently however the membrane lies entirely beneath the skin, here thinner than elsewhere on the head, as in the tortoise. The lacerta agilis, or basking lizard, alone, which lives entirely on the land, has the membrane naked to the air. In this class of animals the columella is not directed forwards to the angle of the jaw as in serpents, but is attached by a cartilaginous extremity to the centre of the membrana tympani, and thus conveys the collected effect of its vibrations directly to the fenestra ovalis: the effect of this arrangement in rendering the impression of sound more definite must be obvious. In some species the cartilaginous portion of the columella is joined to the bony portion at an acute angle, like the letter V, which adds an elasticity to the mechanism very serviceable as a protection to the delicate parts within the fenestra ovalis from the injury they might otherwise sustain by a blow or undue pressure upon the membrana tympani. This is the case with the lizard mentioned above, in which there is also a rudiment of the muscle which serves in the higher animals to tighten the membrane; a circumstance which makes this elbow in the columella a still more essential provision against sudden changes in the distance between the centre of the membrane and the fenestra ovalis. It is worthy of remark that in one class of serpents, the cæcilia (blindworms), the ear is as complete as in any of the fourfooted terrestrial reptiles; possessing a tympanum with its angle. This departure from the usual rule in serpents appears to be one of those compensations so frequently met with in the animal kingdom, the organ of sight in the cæcilia being imperfectly developed.

The acoustic nerve is distributed in two principal branches only to the sacs and the ampullæ; chiefly to the latter, to which it gives a white colour. The filaments form a fine net-work on the outside of the ampullæ, and then piercing their parietes, are raised up within into a kind of crescentic screen, in order probably that they may be more exposed to the impulse of the vibrations descending along the aque-membranes, a Eustachian tube, and a columella bent to an ous endolymph of the semicircular tubes. All the parts we have described are transparent, except the opaque ampullæ and the solid cretaceous otolithes. We have been particular in our account of these membranous parts, which are found with little essential variation in all the superior animals, man included, because in the cartilaginous fishes they admit of more easy examination from their great size and firmer texture, and from the softness of the cartilage that encloses them. In man and the mammalia, they are not only much smaller and more delicate, but encased in the hardest bone in the body, from which it is almost impossible to separate them with sufficient accuracy to be certain that the description is correct.

In some cartilaginous fishes, as the sturgeon, the fenestra ovalis is not closed by a membrane, but by a round buttonlike piece of semi-transparent cartilage, called an operculum, or lid.t

The parts are similar in the osseous fishes, except that they have generally no fenestra ovalis.

In serpents there is but one sacculus containing chalky
Scarpa de Auditu.

This is also found in the aquatic salamander, which, as concerns the organ of hearing, may be considered as the link between fish and reptiles, resembing the latter in the arrangement of the labyrinth, but being unprovided with a tympanum or a columella.

In birds, besides a greater nicety and tenuity in the conformation of the parts hitherto described, the ear is furnished with two additional provisions, both probably of great consequence to the perfection of the organ. The first is a short meatus auditorius externus, or outer passage, which removes the delicate membrane of the tympanum to some depth from the surface of the head, and thus places it more securely, and at the same time, to greater advantage for observing the direction of sound. The other additional provision in birds is an appendage to the mechanism of the internal ear. This is a small conical cavity in the bone, somewhat curved, with a double spiral ridge winding round the interior, and enclosing a cartilaginous structure so corresponding in form with the ridge as to divide the cavity into two partitions. These communicate with another at the apex, and with the vestibule and tympanum respectively, at their other ends. The cavity is termed the cochlea, from its resemblance to a spiral shell; the partition communicating with the internal ear is the scala (winding stair) of the vestibule; the other is the scala tympani; the open

As we have already said, it is only in this last-mentioned class of animals that the ear reaches its complete development. It is nearly the same in all of them; the difference being only in the comparative size and shape of the component parts of the organ, and not in their essential structure, number, or arrangement.

ing from the latter into the tympanum is called the foramen narrower into the vestibule, the superior and larger into rotundum; it is closed by a membrane to exclude the air of the tympanum; each scala taking two turns and a half that cavity while it permits the transit of vibration to or round the modiolus in ascending from the base of the from the vestibular perilymph within; for that fluid, pass-cochlea to the cupola, or inverted cup-shaped cavity at the ing up the cochlea by the scala vestibuli, descends the scala summit, placed over the funnel (infundibulum) into which tympani, and bathes the inner surface of the membrane of the top of the modiolus expands. The cochlea is on a level the fenestra rotunda. The cartilaginous newel is kept in its with the vestibule and anterior to it, the base being turned place like the semicircular tubes by retiform filaments, and towards the meatus internus; the summit looking outwards is supplied with a separate branch of the acoustic nerve, and a little downwards, is turned towards the sudden bend which ramifies and expands on its surface. The lapilli, of the wide canal in the petrous portion of the temporal which seem to be chiefly a provision for hearing under bone by which the internal carotid artery enters the cavity water, and are therefore large and solid in aquatic and am- of the head. It is the close neighbourhood of this artery as phibious animals, appear in birds only as fine crystallized it passes through the compact bone that occasions the rushgrains of chalk in the utricle, or sinus of the vestibule, ren- ing sound of the pulse to be heard when the ear is placed dering the endolymph somewhat turbid. The columella is upon a pillow, or the attention is led to dwell upon what straight, and the membrana tympani pressed outwards by it passes within, by deafness arising from some cause not is consequently convex. There is a crescentic fold of skin affecting the parts essential to hearing. The modiolus is extending upwards from the superior margin of the meatus hollow to some distance from the base. Up this tubular externus, sometimes furnished, as in the horned owl, with a cavity rises the large cochlear branch of the acoustic nerve, fringe of feathers which can be spread at pleasure like a giving off lateral filaments through minute openings arfan to catch the sound. This fold of skin is a rudiment of ranged spirally, which pass through the light spongy bone, the concha, or outer ear, of the mammalia. and emerge from different points on the spiral floors and sides of the scale, where they ramify in a delicate pulpy expansion upon the membranous tubes which line the spiral osseous canals: the rest of the cochlear nerve passes through capillary perforations in the cul-de-sac of the tubular cavity; and ascending in the substance of the central pillar of the modiolus, is distributed through the bone in a similar way to the upper turns of the cochlea and the infundibulum. The two other branches of the acoustic nerve are distributed to the vestibular sac, which lies in a round depression or pit in the barrel-shaped cavity of the vestibule, and to the ampullæ of the semicircular tubes. The latter all meet in a membranous sinus, or utricle, which occupies another distinct pit of the vestibule, called, from its shape, the elliptic fovea, much according to the arrange ment already described in other animals. The principal opening from the vestibule is the fenestra ovalis, situated on the outer side towards the tympanum, which is closed by a membrane; at the lower and front part there is another opening into the scala vestibuli of the cochlea. There are five at its posterior and outer side, which lead into the semicircular canals, of which the superior and posterior enter the vestibule by a common foramen. The sac and utricle each contain a cretaceous deposit, which, in some of the lower mammalia, has the consistence of soft chalk. The cochlea and semicircular canals, from their complexity, are termed the labyrinth. With respect to the object of their peculiar arrangement, not even a probable conjecture has been hazarded. Yet they appear with surprising uniformity in all the mammalia, and some of them, as we have seen, in the more numerous tribes of birds, reptiles, and fishes. The bony canals of the labyrinth and vestibule are stated to be invested within by a delicate periosteum, the surface of which towards the perilymph is thought to be of the nature of a serous membrane, and to secrete that fluid.

We shall therefore describe the organ in one species only. There is every reason to suppose that in hearing, as in sight, man has no superiority over many of the lower animals except what arises from that intellectual supremacy which enables him to discriminate and compare his sensations more justly than they can do. Indeed, it is certain that in the mere perception of sounds he is inferior to most of the mammalia, and probably to birds; and if the musical faculty should seem to imply a greater perfection of the organ, the error, for such we believe it to be, may perhaps disappear upon reflection. We therefore select the human ear as the type of the organ in mammalia, not because it is in any respect more complete than the rest, but as the most interesting. The same description, of the more important parts at least, might be applied, nearly word for word, to all. The parts now to be described fall naturally under a three-fold division into the internal, middle, and external ear. 1. The internal ear, comprising the acoustic nerve, vestibule, and labyrinth, is deeply placed in the interior of the head, within the most compact and hardest of the bones, denominated from that circumstance the petrous or rocky portion of the temporal bone. This wedge-like or triangular projection passes obliquely inward and forward in the direction of the outer tube of the ear, forming a strongly-marked knobby ridge within the cranium, in the basis or floor of that cavity. Near the inner point, which nearly meets its fellow on the other side, and upon its posterior declivity, there is a large trumpet-like hole (meatus auditorius internus) into which the seventh cerebral nerve enters from the medulla oblongata. [BRAIN, NERVE.] The meatus passes in a direction outwards, and therefore obliquely, into the petrous portion for half an inch, and then terminates abruptly in two fovea, or pits: from the upper of these goes a winding canal through the substance of the bone, which is the course of the motor nerve of the face (the portio dura of the seventh pair), which, here separating from the auditory nerve, or portio mollis, we need not follow. The latter, splitting into several sets of filaments, finds its way through small sieve-like openings at the bottom of the lower fovea into the internal ear, and is here distributed in three separate portions to the cochlea, the ampullæ of the semicircular tubes, and the utricle, or vestibular sac. The cochlea is more complicated than in birds; it consists of a spiral canal in the bone, gradually diminishing as it ascends to a point, wound round a central hollow pillar of bone, called the modiolus, or newel. From its inner surface, that, namely, which may be considered as a groove in the modiolus, a thin and spongy lamella of bone projects rather more than half across the canal, ascending in a similar spiral. From the edge of this lamella (called the lamina spiralis) a membrane passes to the outer surface of the canal, where it is attached; thus completing the separation of the canal into two scale, or winding partitions, which unite at the summit, and open (as before), the lower and

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The deafness which arises from causes which affect the fenestra ovalis, or the nerves and canals within the vestibule and labyrinth, is seldom or never cured; and it is unfortunately very common. There is a very easy way by which the nature of the case may be often sufficiently tested. If the internal ear be affected, especially the nerves of it, the ticking of a watch pressed against the teeth or the outer part of the head on that side, will be very obscurely distinguished. If not, the sound can be easily heard, as the solid bones interposed between the sonorous body and the nerve are excellent conductors of vibration.

2. The middle ear comprises the cavity of the tympanum' with its contents; the cells in the bony prominence behind the ear, called the mastoid process, with which the tympanum communicates; and the Eustachian tube, or passage leading from the tympanum into the upper and back part of the throat, where it opens in the form of an expanded slit on each side behind the posterior nares.

The tympanum is an irregular cavity scooped in the petrous portion of the temporal bone between the vestibule and the external meatus. The principal entrances to it are the fenestra ovalis and the round or somewhat oval opening at the bottom of the external passage upon which the membrana tympana is stretched. Between these there is extended a chain of three small bones, obliquely articulated to each other with perfect joints, so placed that the chain somewhat resembles in figure the letter Z.

These bones are called respectively the stapes (stirrup), the incus (anvil), and malleus (hammer), from some similarity in form to those implements. The base of the stapes is applied to the fenestra ovalis, exactly fitting it, and is attached firmly to its membrane. The extremity of the longer leg of the incus is articulated to the head of the stapes, and there is a minute bone between them of the size of a small shot, which is generally considered to be only a process of the incus. It is however called from its spherical shape the os orbiculare, and is sometimes reckoned as a fourth bone. (Fig. 3, 0.) The shorter leg of the incus (fig. 2, c,) rests against the bony parietes of the tympanum at the back part, near the mastoid cells. Upon the hollowed cavity in the head of the incus (fig. 2, a) the lateral depression of the head of the malleus (fig. 2, k) is articulated, and moves easily; the long handle of the latter is attached by its extremity (fig. 2, h) to the middle of the membrana tympani, as well as by a portion of the side of the handle, which lies close to and parallel with the membrane. The long slender process of the malleus called the processus gracilis (fig. 2. g) lies in a slit passing to the articulation of the jaw called the glenoid fissure.

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Fig. 2. Magnified view of the ossicula auditûs. M, malleus; I. incus; S, stapes; o, shape of the fenestra ovalis; a, cavity of the incus, which is articulated to the malleus; d, longer process of the incus with the os orbiculare attached at b; c, its shorter process; e, head of the malleus; f. its short process, or prominent point for the attachment of the tensor tympani; &, the depression which articulates with the incus; g, processus gracilis of the Inalleus; h, its handle, or manubrium.

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most reptiles; this is to permit the membrana tympani to
be drawn into a conical shape so as to tighten it, and adapt it
either to resist the impulse of too loud a sound, or favour a
more acute or gentle one.
The muscle which chiefly
effects this object, called the tensor tympani (fig. 4, a), is
attached near the head of the malleus to a point projecting
from it. (Fig. 2, f.) Other muscles, to steady and antagonize
its action, called the laxator major and minor tympani
are also attached to the malleus, the former (fig. 4, b) to
the processus gracilis, the latter (fig. 4, c) to the handle of

Fig. 4.

Fig. 4. Muscles attached to the ossicula auditús. a, tensor tympani; b, laxator major; e, laxator minor; d, stapideus. the bone. A further description of the directions and outer attachments of these minute muscles would be tedious and unintelligible to the general reader. No muscle is attached to the incus, but a small one of great importance is inserted into the neck of the stapes, called the stapideus; the effect of this is to counteract the obliquity of traction or tilting of the stapes, which would otherwise ensue from the movements of the other bones; by this means the motion of the stapes is directed either immediately to or from the fenestra ovalis, the membrane of which is also further preserved from injury by the oblique arrangement of the joints of these minute bones, by means of which, although the membrane of the tympanum oscillates through a consider able space in passing from tension to relaxation, that of the fenestra is moved to a much smaller extent. It is to be observed that the same action which draws the membrana tympani into a cone thrusts the base of the stapes farther into the fenestra ovalis.

These small muscles are not under the dominion of the will, being supplied with nerves in a way peculiarly interesting to a physiologist, and acting automatically in correspondence with the impressions on the auditory nerve. Yet the instinctive consciousness we have of the degree of their contractions in adjusting the tension of the membrana tympani to circumstances, is probably one of our chief means of estimating the intensity of sounds.

The fenestra ovalis is situated nearly opposite the membrana tympaní, on the upper edge of a prominence called the promontory; it faces outwards and a little downwards; and beneath it, concealed by the promontory, is the foramen rotundum, closed by a membrane, and leading into the cochlea by the scala tympani. The object of this last opening is disputed: some think it conveys in part the vibrations of the air of the tympanum to the internal ear; but it seems more reasonable to suppose, with Sir C. Bell, that the end it chiefly serves is to give vent and freedom to those of the fluids pent up in the unyielding bony canals of the labyrinth. Besides these openings from the tympanum, there are others which lead into the mastoid cells behind it; these are also filled with air, and are supposed to contribute to the distinctness of the tympanic vibrations. There is also an opening from the tympanum forwards into the Eustachian tube. This canal is nearly two inches long the first part of its course from the tympanum is bony: it then becomes cartilaginous, and widens as it approaches the throat, the mucous membrane of which lines it, and thence passing into the tympanum, spreads over the surface of the whole cavity, investing the ossicula and its other contents, as well as the mastoid cells. From this circumstance arises the tendency of the inflammation of cold or sore throat to extend into the tympanum, producing temporary deafness, ear-ache, and sometimes mischief of a more permanent kind. From the deafness which accompanies the closure of the Eustachian tube by that or other causes, the importance of its functions in renewing and giving vent to the air within the tympanum may be appreciated. Besides the foramina already mentioned, there are others through which nerves and vessels enter the tympanum. We have not space to describe them: we shall only mention that one of the nerves, called the chorda tympani, originally connected with the portio dura of the seventh nerve, after traversing the petrous

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