charge of cannon, remains for some time insensible to weak sounds; as the eye, exposed to strong light, becomes for some time unsusceptible of the impressions of weak light. According to what has now been stated, the course of vibrations is from the external ear, along the auditory passage to the membrane of the drum; from thence along the chain of bones to the membrane of the oval fenestra, situated in the partition between the drum and the labyrinth, the latter being the peculiar seat of audition, as the posterior chamber of the eye is the peculiar seat of vision. Sounds, however, may reach the labyrinth by other channels than this, the proper course; and therefore complete deafness does not occur even when the membrane of the drum and the ossicles are totally destroyed, provided the membrane of the oval fenestra re mains entire, so that it retains the contents of the labyrinth. Thus, vibrations communicated to the skull are conveyed to the labyrinth directly. Whatever tends to increase the impetus of the circulation may be accompanied with distinct perception of the pulsations of the internal carotid artery, which enters the skull through a canal in the petrous portion of the temporal bone; and when the sensibility of the ear is morbidly augmented, each beat of this artery becomes distinctly audible. When a watch is held in the mouth, without touching the teeth, the ticking is indistinctly heard, but in contact with the teeth it is rendered very perceptible.

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The Labyrinth.-This is the proper audience-chamber of the ear. It is entirely surrounded with hard trous bone, and consists of several intricate winding galleries, which have suggested the name applied to it. Our engraving, representing a view of the labyrinth, magnified, where the different passages are seen laid open, will convey a better idea of the different parts than a detailed description could do. The labyrinth consists of the vestibule or lobby, marked a a a; of three semicircular canals, named, according to their relative position, the inferior,

superior, and posterior, the first marked bb, the second cc, and the third dd. Each limb of these canals opens into the vestibule separately. These orifices are marked 1, 2, 3, and 4, excepting one limb of the superior, and another of the posterior, which terminate in a common canal, e, opening at 5. The third portion of the labyrinth

resembles in form the shell of a snail, from which circumstance it has obtained the name of cochlea. The cochlea consists of two spiral canals, which wind round a central pillar two times and a half. These canals are separated by a spiral partition; they communicate however at the summit, where they are covered by what is termed the cupola. One of these canals or staircases commences in the vestibule, and ascends spirally to the cupola, marked hhhhh. The other, gggg, may be considered as commencing at the cupola, descending till it terminates at the round fenestra of the drum, from which it is separated by the membrane of that orifice.

This intricate and curiously constructed part of the apparatus of hearing is lined throughout by a membrane which secretes a somewhat viscid and limpid fluid, in which terminate the delicate pulpy extreme divisions of the auditory nerve, somewhat in the same manner as the retina is spread out upon the choroid coat of the eye. Besides, there are little vesicles filled with a transparent fluid, much smaller in their diameters than the several canals they occupy. These fill up the central spaces, and may be compared to the vitreous humour of the eye, serving to support the delicate auditory nerve, as that supports the expanded retina. At the same time, they are admirably fitted for receiving and communicating the vibratory impressions to the nervous fringes. been supposed that the use of that canal of the cochlea, which terminates at the oval fenestra, is to admit of the undulation of the fluid contents of the labyrinth, where the vibrations communicated through the oval fenestra circulate along the winding passages, pass up the spiral staircase of the cochlea, leading from the vestibule to the cupola, and from the cupola down the other staircase to the round fenestra, the membrane of which yields to the impulse, and again, by its elasticity, returns the vibration. in the opposite direction.

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The fifth cranial nerve, associated with filaments from the facial nerve, contribute the nervous twigs to the internal ear; the former imparting common sensibility to the different parts, as the filaments from the same nerve send branches to the interior of the eye for a similar purpose; the latter commanding the movements of the muscles of the chain, so as to bring them into action with due force in the necessary state of combination, and likewise supplying the muscles of the auricle. Thus we find the peculiar sensibility of the ear depends on the auditory, the common sensibility on the fifth, and the voluntary and instinctive movements on the facial, nerve.

Fig. 37 is intended to convey a general idea of the

relative position of the different parts of this interesting organ, which we have endeavoured to describe. a is the pavilion of the external ear, b the lobe, c the external auditory passage, d the membrane of the drum, e the cavity of the drum, f the Eustachian tube, g the oval fenestra, h the round fenestra, i the vestibule, k the cochlea, 7 the auditory nerve, on its passage to the labyrinth, M the semicircular canals.

From what has been stated, it will be perceived that every part of this delicate instrument combines with every other with the utmost nicety and accuracy; that the pavilion is constructed for the reception and transmission of vibrations from without to the drum, where they are subjected to various modulations, and subsequently conveyed to the labyrinth, the immediate seat of the auditory nerve; that from this chamber the impressions from the vibrations are communicated backwards to the origin of

the auditory nerve, at the posterior surface of the medulla oblongata, the centre of the cerebro-spinal portion of the nervous system; and lastly, that they become objects of perception to the mind through the medium of the cerebrum. But how they should impress the delicate extremities of the auditory nerve, how they are conveyed by it to the brain, or of what nature is the communication between the matter of the brain and the mind, we are entirely ignorant, and in all probability, in our present state of existence, will ever remain so.

In vain also shall we attempt to account for the pleasurable sensations derived from the various combinations of sound which constitute music,-music being one of those combinations of material and mental conditions from which we, in our material and mental relations, derive more or less gratification according to our individual characters. It will be time enough for us to explain, by material causes, how one person is so sensibly affected by music to which another, under the same apparent circumstances, seems to be altogether indifferent, when we become able, on material principles, in a satisfactory manner, to account for peculiarities which distinguish the individuals of the human race. It is sufficiently well known that the gratification arising from music depends to a very considerable extent upon association of ideas, on education, and even upon transient, accidental, and apparently trivial circumstances, the investigation of which is more calculated to gratify the fancy than improve the judgment.