THE SENSE OP HEARING. 



231 



quantity of oil, collected in their cells. To compensate for 

 this soft structure, whales are furnished with a sounding 

 board, or the dense conch, above mentioned. In fishes, we 

 often find several of these little bony concretions, of a smooth 

 and polished appearance, and hard and brittle as porcelain. 

 These are often seen in cutting up boiled fish, when placed 

 upon the table, but few are aware of the uses they serve in 

 perfecting the organ of hearing. 



11. In order, however, to understand the precise function 

 of these bones, it will be necessary to examine a little more 

 into their situation and connection. In the following plan, 

 they are represented, greatly magnified, but each bone in its 



natural position. 



Fig. 4. 



A, the malleus, or mallet, with its long handle running down, to 

 touch with its delicate extremity the membrane of the drum. B, is the 

 incus, or anvil, nicely fitted to the mallet, and showing C, the orbicular 

 bone placed between its termination, and D, the stirrup. The line a, b, 

 represents the centre of motion of the malleus, and c, d, the centre of 

 motion of the incus. Now this chain of bones acts on the principle of 

 a long lever, as a small motion at one end of a long pole serve to move 

 it through a wide space at the other. As Sir Charles Bell explains it, 

 the head of the malleus is so articulated with the body of the incus, 

 that the centre of motion of the incus is a line drawn through the centre 

 of its body, and consequently the extremity of the long process, to 



