ANIMAL MECHANISM, 



The remaining parts, beyond the boundary of the membrane, re- 

 main to be described, particularly, although represented here for the 

 sake of keeping up the connexion of parts in the mind. 

 /, g, /i The malleus; f its handle ; g its long handle; h the head 



or bulb. 



i, k inchus, or anvil; i short, and k, long processes, m stapes. 

 V, H, A, m, n,p, The labyrinth; n,p the cochlea, n the begin- 

 ning, p termination, m the vestibulum. 



NOTE. I have found immense difficulty in demonstrating this or- 

 gan, without very large models: one now in my cabinet, made of 

 wood, magnifies the internal ear three feet, which can be seen and 

 understood in all its relations. Formerly, when I taught anatomy 

 at the Berkshire Medical Institution, it was customary to suppose 

 the medical college an ear, and thus, illustrate its intricacies, by 

 constant reference to the apartments and passage ways of that 

 edifice. 



THE DRUM, Oil MEMBRANA TYMPANI. (*) 



From the foregoing description of the mcatus or canal, 

 the exact locality of the drum head will be understood. 

 Fitted to the rim of bone, in a manner similar to the 

 parchment over the barrel of a snare drum, it is kept 

 perfectly tense, but by an arrangement of fibres peculiar 

 to its organization, which is not clearly comprehended 

 by anatomists. It is oval in shape, and somewhat con- 

 cave outwardly, and so transparent and thin, that objects 

 can be seen through it, being of the color of white oiled 

 paper ; any person of common ingenuity, can dissect this 

 beautiful membrane in the head of a dead fowl, in five 

 minutes, with the point of a knife. It then presents a 

 striking resemblance to a battledoor. This closes up 

 the extremity of the tube, in a healthy ear ; notwithstand- 

 ing, it is frequently ruptured by the firing of heavy guns, 

 inflammation, and other accidents, without producing 

 deafness. Across this drum, a fine thread of a nerve is 

 drawn, called corda tympani, which gives it the requisite 

 sensibility and connexion with the system of sensation. 



(l) Lobsters, crabs, and in fact, all that remarkable class of ani- 

 mals, whose skeletons are outside of the body, in the form of a shell, 

 have their ears placed at the extremities of projecting points. The 

 lobster's can be detected at the end of a short stump, near the root 

 of the long feelers it consists of a perforated bony papilla, having 

 a membrane stretched over it, covering a drop of fluid, in which 

 floats the auditory nerve. 



