The annexed diagram may render it easier to follow the description.

The structure which is to admit Sound as a visitor is protected and ornamented at its entrance by a light movable awning (the external ear). Beneath and within this opens a recess or passage (meatus auditorius externus), at the farther end of which is the parchment-like frontdoor, D (membrana tympani).

Beyond this is the hall or entry, H, (cavity of the tympanum,) which has a ventilator, V, (Eustachian tube,) communicating with the outer air, and two windows, one oval, o, (fenestra ovalis,) one round, r, (fenestra rotunda,) both filled with parchment-like membrane, and

looking upon the inner suite of apartments (labyrinth).

This inner suite of apartments consists of an antechamber, A, (vestibule,) an arched chamber, B, (semicircular canals,) and a spiral chamber, S, (cochlea,) with a partition, P, dividing it across, except for a small opening at one end. The antechamber opens freely into the arched chamber, and into one side of the partitioned spiral chamber. The other side of this spiral chamber looks on the hall by the round window already mentioned; the oval window looking on the hall belongs to the antechamber. From the front-door to the oval window of the antechamber extends a chain, c, (ossicula auditûs,) so connected that a knock on the first is transmitted instantly to the second. But as the round window of the spiral chamber looks into the hall, the knock at the front door will also make itself heard at and through that window, being conveyed along the hall.

In each division of the inner suite of apartments are the watchmen, (branches of the auditory nerve,) listening for the approach of

Sound. The visitor at length enters the porch, and knocks at the front-door. The watchmen in the antechamber hear the blow close to them, as it is repeated, through the chain, on the window of their apartment. The impulse travels onward into the arched chamber, and startles its tenants. It is transmitted into one half of the partioned spiral chamber, and rouses the recumbent guardians in that apartment. Some portion of it even passes the small opening in the partition, and reaches the watchmen in the other half of the room. But they also hear it through the round window, not as it comes through the chain, but as it resounds along the hall.

Thus the summons of Sound reaches all the watchmen, but not all of them through the same channels or with the same force. It is not known how their several precise duties are apportioned, but it seems probable that the watchmen in the spiral chamber observe the pitch of the audible impulse which reaches them, while the others take cognizance of its intensity and perhaps of its direction.

Such is the plan of the organ of hearing, as an architect might describe it. But the details of its special furnishing are so intricate and minute that no anatomist has proved equal to their entire and exhaustive delineation. A titled observer, the Marquis Corti, has hitherto proved most successful in describing the wonderful key-board found in the spiral chamber, the complex and symmetrical beauty of which is absolutely astonishing to those who study it by the aid of the microscope. The figure annexed shows a small portion of this extraordinary structure. It is from Kölliker's well-known work on Microscopic Anatomy.

Enough has been said to show that the ear is as carefully adjusted to respond to the blended

impressions of sound as the eye to receive the mingled rays of light; and that as the telescope presupposes the lens and the retina, so the organ presupposes the resonant membranes, the labyrinthine chambers, and the delicately suspended or exquisitely spread-out nervous filaments of that other organ, whose builder is the Architect of the universe, and the Master of all its harmonies.

Not less an object of wonder is that curious piece of mechanism, the most perfect, within its limited range of powers, of all musical instruments, the organ of the human voice. It is the highest triumph of our artificial contrivances to reach a tone like that of a singer, and among a hundred organ-stops none excites such admiration as the vox humana; a brief account of the. vocal organ will not, therefore, be out of place.

The principles of the action of the larynx are easily illustrated by reference to the simpler musical instruments. In a flute or flageolet the musical sound is produced by the vibration of a column of air contained in its interior. In a clarinet or a bassoon another source of sound