subserve to our comfort and pleasure, but are instrumental in
promoting our intellectual enjoyments. The organ of hearing, or the
ear, is one of the most complicated in the human body.

ANATOMY OF THE ORGANS OF HEARING.

944. The EAR is composed of three parts: 1st. The _External Ear._ 2d.
The _Tym'pan-um_, or middle ear. 3d. The _La'by-rinth_, or internal
ear.

945. The EXTERNAL EAR is composed of two parts: The _Pin'na_,
(pavilion of the ear,) and the _Me-a'tus Aud-it-o'ri-us Ex-ter'nus_,
(auditory canal.)

946. The PINNA is a cartilaginous plate which surrounds the entrance
of the auditory canal. It presents many ridges and furrows, arising
from the folds of the cartilage that form it.

_Observation._ The pinna, in many animals, is movable; in those that
pursue their prey, it is generally directed forward; in timid animals,
as the hare and rabbit, it is directed backward. In man, this part is
but slightly under the control of the will.

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943. What is said of the importance of hearing? Is the ear complicated
in its structure? 944-962. _Give the anatomy of the organs of
hearing._ 944. Of how many parts is the ear composed? Name them. 945.
Give the parts of the external ear. 946. Describe the pinna. What is
said in reference to the pinna of many animals?

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947. The MEATUS AUDITORIUS is a canal partly cartilaginous, and partly
bony, about an inch in length, which extends inward from the pinna to
the _Mem'bra-na Tym'pan-i_, (drum of the ear.) It is narrower in the
middle than at the extremities. It is lined by an extremely thin pouch
of cuticle, which, when withdrawn, after maceration, preserves the
form of the canal. Some stiff, short hairs are also found in the
interior of the channel, which stretch across the tube, and prevent
the ingress of insects. Beneath the cuticle are a number of small
follicles, which secrete the wax of the ear.

[Illustration: Fig. 144. A representation of the four bones of the ear.
The smallest is highly magnified. This bone is early matured, and in the
adult it becomes united with the incus. These bones are retained in their
places and moved by three ligaments and four muscles.]

948. The MEMBRANA TYMPANI is a thin, semi-transparent membrane, of an
oval shape. It is about three eighths of an inch in diameter, and is
inserted into a groove around the circumference of the meatus, near
its termination. This membrane is placed