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not governed, Mr. Carlisle says, by the form, habits, or voice of the 

 animal, except in those mammalia which inhabit the waters, such as 

 the seal, the walrus, and the whale tribe : in these the stapes is more 

 massive ; but in the otter, which only dives occasionally, the stapes 

 does not differ from that of the fox. In the tiger, the dog, and other 

 ferae, the crura are straight, and meet in an acute angle ; but the 

 same figure occurs in the horse, in the beaver, in the goat, and in 

 many other herbivorous quadrupeds. In the cete, the muscle of the 

 stapes pulls the capitulum at such an angle, as very much to depress 

 its subjacent end into the fenestra vestibuli ; and the joint appears 

 capable of considerable motion. In the walrus, this ossicle is entirely 

 solid : in the seal, and in the cete, the bone has only a small per- 

 foration instead of the crural arch. 



Mr. Carlisle has discovered a very remarkable singularity in the 

 stapes of the marmot, and in that of the guinea-pig. In those ani- 

 mals, the bone is formed of slender crura, constituting a rounded 

 arch : through this arch an osseous bolt passes, so as to rivet it to 

 its situation. This bolt, to which Mr. Carlisle has given the name 

 of Pessulus, is placed near the top of the arch, so that, by the action 

 of the stapedeus muscle, the upper part of the straight cms is brought 

 into contact with the pessulus. The use of this mechanism is not 

 obvious, there being nothing in these animals, excepting their shrill 

 whistle, peculiarly different from others which are destitute of such 

 mechanism. In the kanguroo, the stapes is like the corresponding 

 ossicle in birds, called Columella. In the two species of Ornitho- 

 rhynchus (paradoxus and hystrix), this resemblance to the columella 

 is still more striking, and forms an additional point of similarity be- 

 tween these singular quadrupeds and birds. These columellae are 

 articulated to a small bone, which performs the office of the manu- 

 brium of the malleus ; whereas, in birds, the capitulum of the colu- 

 mella is slightly expanded, and is joined to a triangular plate of car- 

 tilage attached to the membrana tympani. In some birds, a small 

 foramen occurs in the middle of this plate. 



The amphibia are provided with columellse similar to those of birds; 

 but the cartilage is united to the under surface of the true skin, with- 

 out any apparent application of muscles to alter its tension. 



From the preceding circumstances, Mr. Carlisle is led, he says, to 

 the following conclusions : In man, and in most of the mammalia, 

 the figure of the stapes is an accommodation to that degree of light- 

 ness which seems a requisite condition ; and that bone is especially 

 designed to press on the fluid contained in the labyrinth ; the ulti- 

 mate effect of which pressure is, an increase of the tension of the 

 membrane closing the fenestra cochleae. 



There does not, in Mr. Carlisle's opinion, appear to exist any 

 motion between the ossicula auditus that bears any relation to the 

 peculiar vibration of sounds. He rather conceives, that the different 

 motions of these bones only affect the membrana tympani, so as to 

 lessen the intensity of violent impulses. Sounds of less impetus, not 



