Mr. Carlisle on the Physiology of the Stapes. 203 
muscle of the malleus rotates the incus hack again, and restores 
it to its passive perpendicular situation ; becoming on such 
occasions the antagonist of the stapedeus. It is worthy of 
remark, that all the muscles of the ossicula auditus act nearly at 
right angles, or in straight lines, contrary to the ordinary 
course of muscular application, by which their forces are com- 
paratively augmented. 
The varieties in the human stapes are few : they appear in 
the relative curvature of the crura, and in the degree of slen- 
derness or symmetry of its general form. 
The fenestra vestibuli admits the basis of the stapes to 
pass into the vestibulum, when the connecting membrane is 
destroyed, there being no other obstacle to its descent. 
None of the external similitudes in form, nor any corre- 
spondence in the habits, or voices of animals, appear to govern 
the configuration of these ossicles, except in those mammalia 
inhabiting the waters, such as the seal, walrus, and whale 
tribes,* where the stapes is always more massive : but in the 
otter, which only dives occasionally, the stapes does not vary 
from that of the fox. I11 the tiger, dog, and other feras, the 
crura are straight, meeting in an acute angle ; but the same 
figure occurs in the horse, beaver, goat, and many more her- 
bivorous quadrupeds ; so that no inference can be drawn from 
these different habits of life. 
In the cete, exemplified in the Plate by the porpoise, whose 
organs of hearing precisely resemble those of whales which 
I have seen, and agree with the descriptions of others by Pro- 
fessor Camper, the muscle of the stapes pulls the capitulum 
at an angle of 45 degrees, with the plane of the basis, so as 
* I have not had an opportunity of examining the ossicles of a hippopotamus. 
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