er 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 auditus_,) 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 partitioned 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. An Italian nobleman, 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
absolute