THE HUMAN EAR.

The ear consists of three principal divisions, viz. the external, intermediate, and internal ear.  The different parts of the first division, or external ear, are described by anatomists under the name of the helix, antihelix, tragus, antitragus, the lobe, cavitas innominata, the scapha, and the concha.  In the middle of the external ear is the meatus, or passage, which varies in length in different individuals.  The external or outward ear is designed by nature to stand prominent, and to bear its proportion in the symmetry of the head, but in Europe it is greatly flattened by the pressure of the dress; it consists chiefly of elastic cartilage, formed with different hollows, or sinuosities, all leading into each other, and finally terminating in the concha, or immediate opening into the tube of the ear.  This form is admirably adapted for the reception of sound, for collecting and retaining it, so that it may not pass off, or be sent too rapidly to the seat of the impression.  There have been a few instances of men who had the power of moving the external ear in a similar manner to that of animals; but these instances are very rare, and rather deviations from the general structure; nor did it appear in these instances that such individuals heard more acutely:  a proof that such a structure would be of no advantage to the human subject.  With respect to the external ear in man, whether it is completely removed either by accident or design, deafness ensues, although its partial removal is not attended with this inconvenience:  the external ear, therefore, or something in its form to collect sound, is a necessary part of the organ.

The next division is the intermediate ear; it consists of the tympanum, mastoid cells, and Eustachian tube.  The tympanum contains four small delicate bones, viz. the malleus, the incus, the stapes, and the os orbiculare, joined to the incus.  The intermediate ear displays an irregular cavity, having a membrane, called the membrana tympani, stretched across its extremity; and this cavity has a communication with the external air, through the Eustachian tube, which leads into the fauces, or throat.  The membrane of the tympanum is intended to carry the vibrations of the atmosphere, collected by the outward ear, to the chain of bones which form the peculiar mechanism of the tympanum.  Besides the effect of the hard and bony parts of the ear in increasing the power of sound, the tension of the different membranes is also a requisite:  thus various muscles are so situated as to put the membrane on the stretch, that the sound, striking upon it, may, from its tension, similar to that of the parchment of a drum-head, have full influence upon the sense.  In respect to its tension, the membrane of the tympanum may be also compared, not unaptly, to the string of a violin, or musical instrument, even more properly than to a drum; as the state of tension and relaxation in such chords produces a variety of