236 ANIMAL MECHANISM. 



also dsstitute of an external accompaniment of the inner 

 organ, and yet all these families, including the amphibi- 

 ous, as frogs, turtles and the like, have a beautifully con- 

 structed internal ear, as remarkable, so far as a mechani- 

 *cal arrangement of parts is concerned, in conveying the 

 pulsation of sound, as that of the most favored musician. 

 In the sequel, it will be noticed that the common skin of 

 their bodies, drawn as it is over the opening in the head, 

 answers two important offices in the function of hearing. 



EAR TUBE.* 



When the temporal or side bone of the head, contain- 

 ing, entirely, the internal ear, is carefully sawed in twain, 

 the canal, of which we are speaking, will be found about 

 three quarters of an inch in length, and somewhat coni- 

 cal, being contracted towards its inner extremity and, 

 on an average, a little less than a quarter of an inch in 

 diameter. This passage is a gentle curve, as the tube, 

 from the external opening, rises upward, but at half its 

 length, turns downward again, and there bulges out in 

 shape, something like the bowl of a spoon. A delicate 

 rim, like a moulding rises on the edge of this expanded 

 mouth, for sustaining the drum head, soon to be noticed, 

 very much like the method of nailing a hoop within the 

 mouth of a barrel, near the chime, to keep the head from 

 falling in. To afford greater surface, that the drum 

 head may be considerably larger than the extremity of 

 the tube would allow, were it stretched perpendicularly 

 across, it is sloped, so that it requires an oval cover, under 

 such circumstances, very much larger, than if it were 

 round, and fitted to the square end of the pipe. All this 

 may be examined in the temporal bone of a horse, sheep, 

 or dog's skull, as they are found bleaching in the fields. 

 In these animals, the analogy to the human is particu- 

 larly strikincr. The common skin of the face is carried 

 within the tube, for its lining, but perforated in numerous 

 pFaces, by the ducts of delicate little bags, lying between 

 the bone and skin, which are constantly secreting and 

 pouring out a bitter, nauseous oil or wax. The object of 



*In books, termed tlio Metus auditorius externus, simply 

 meaning the external passage to the inner cavities. 



