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ANIMAL MECHANISM. 



There is a necessity for uncommon delicacy, in their 

 case, as their ear is constructed for hearing with equal 

 precision in water as well as air. ( 2 ) 



INTERNAL EAR. 



All parts beyond the drum head are collectively called 

 the labyrinth, in consequence, probably, of their intri- 

 cacy. 



To understand the arrangement of the apartments to 

 which the reader is now to be introduced, requires pa- 

 tience, as well as close observation, or the mechanism 

 cannot be comprehended. First the 



TYMPANUM. 



Directly beyond the membrane is a small room, of the 

 capacity of a common white bean. Its name is derived 

 from a word, meaning a drum, as it is one in office, 

 but having, instead of one head like the kettle or 

 two as in the snare drum, it has three heads; the 

 argest of which is towards the outer ear, while at the 

 other end of the barrel, are two little ones. 



This labyrinth constitutes the difficulty in studying the 

 anatomy of this part of the system. Three distinct 



(2) In that class of serpents which is covered with scales, the 

 external contrivance of a tense skin over the internal ear, is far infe- 

 rior to the frog or lizard's: to the underside of a cluster of thin 

 scales, wedged in the loose dermoid texture, a slender bone, in 

 in figure like the pestle of a mortar, runs into the tube, towards the 

 brain, and plays into the fenestra ovalis. 



All the varieties of serpents are distinguished for their delicacy 

 in the perception of sound. The boa family, particularly, are 

 those which exhibit the most satisfaction in music. The writer 

 has carefully examined a boa constrictor, which when fully grown, 

 is horrible to the sight, that was inattentive to sounds, except when 

 hungry. At such 'times, the scratch of a pin against the wall, 

 roused the monster to unceasing watchfulness. The ear of the land 

 tortoise, and the rattlesnake, both of which are in my collection, do 

 not differ as much as the physiologist might at first suppose though 

 in the water turtle, constituted for hearing alternately in air and 

 water, there is a perceptible difference. In the first, a single bone 

 is found ; while in the latter, in addition to the bone, there are fine 

 chalky particles, which move against each other, to propagate the 

 motion or noise in the water, to tlie ear containing the ramifications 

 of ihft nerve. 



