The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . ut impressions are produced upon it by means ofmotion in the atmosphere which surrounds is the sense of hearing. Every movement ofevery form of matter gives rise to waves or vibra-tions in the air, which lies in contact with the mov-ing substance. These atmospheric waves are re-ceived, and the impression made by them is trans
The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . ut impressions are produced upon it by means ofmotion in the atmosphere which surrounds is the sense of hearing. Every movement ofevery form of matter gives rise to waves or vibra-tions in the air, which lies in contact with the mov-ing substance. These atmospheric waves are re-ceived, and the impression made by them is trans-mitted to the brain bv a special apparatus. 361. The External Ear.—The ear (Fig. 65) isusually described by anatomists as consisting ofthree divisions—the external ear, the middle ear, andthe internal ear. The appearance of the externalear is familiar to all. It has a somewhat shell-Hkcform, has numerous ridges and hollows, and is com-posed principally of cartilage covered with external ear serves to collect the waves ofsound, and direct them toward the internal animals this organ is very movable, and, during 284 ORGANS OF PERCEPTION. their waking hours, is generally in motion, to catchsound from various directions. In the human be-. FlG. 65.—Section of the ear, showing the relative positions of the external,middle, and internal ear. mg there are three small muscles attached to theexternal ear—one behind, one above, and one infront. These muscles, however, are practically use-less, and very few persons have any voluntary con-trol over them. Those who do, can cause the mus-cle in the rear to contract, and move the ear slightlybackward, but the motion is limited, and answersno purpose. 362. The Middle Ear.—From the external ear acanal passes directly inward, toward the interior ofthe skull, for a distance of about an inch and aquarter. At its inner extremity it is closed by athin membrane, called the membrane of the tympa-num, or the drum of the ear;
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