298 ANIMAL MECHANISM. 



hall or porch of the edifice beyond, from which doors 

 are opening into various winding passages. Its length 

 and diameter are not far from a grain of wheat, as in a 

 preceding paragraph, if we suppose an individual has 

 torn away the stapes from the little drum head, str^fched 

 across the oval window, and then cut away the latter, to 

 wend his way into the vestibule, he will find it a long, 

 but narrow room. ( 5 ) 



On one side he will discover three holes, and on the 

 opposite, only two, which are the openings or communi- 

 cation of the semicircular canals, with the vestibule. 

 Within this vestibule, are two sacs, water tight, contain- 

 ing a clear aqueous fluid. Though there is no commu- 

 nication between the sacs, the quality of the fluids 

 distending them, is alil$ one is considerably larger 

 than the other, and both together, would not equal in 

 bulk, two good sized pin-heads. The one of the greatest 

 magnitude, is called the alvcus communis or the union of 

 rivers from the circumstance that the canals were 

 thought by the old anatomists to resemble streams of 

 water, having a free communication with the water in 

 the reservoir. Saculus Cochlea, the lesser one, though 

 separated from the other by the thickness of its own and 

 the other's walls, is eked out into a long gyrating tube, 

 that traverses the cochlea. 



This large sac, alveus communis, is the elementary one 

 found in polipi and it is this that is built upon from 

 one species to another, till the complicated machinery of 

 the human ear, on dissection, displays it, as the corner 

 stone of the sense of hearing from worms, to the perfect 

 musical ear of man. 



(5) If, by any circumstance, the membrane of the oval windov) 

 or Jenestra avails, be ruptured, the fluid of the labyrinth will cer- 

 tainly escape. This constitutes incurable deafness. No operation, 

 no prescription can avail, as, in the constitution of things, the 

 acoustic nerve cannot be acted upon in any other way, than that 

 through the agitation of the fluid which surrounds it. Dr Darwin 

 was of an opinion that if a deaf person dreamed of hearing, the in- 

 ternal parts, essential to the function, were unimpaired. The same 

 remark is applicable to the blind. I have invariably found that 

 the incurably deaf as well as incurably blind, never ; dream of 

 hearing or seeing. This clearly shows a destruction of the sense, 

 inasmuch as the imagination cannot rouse a single vestige of their 

 former activity. 



