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 415 backward. In man, this part is but slightly under the control of the will.
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?
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 It is lined by an extremely thin pouch of cuticle, which, when withdrawn, after maceration, preserves the form of the canal.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.
Fig. 144.
