426 THE SENSORIAL FUNCTIONS. 



drum, at one end, and with the fenestra ovalis 

 at the other, there extends a chain of very 

 minute moveable bones, seen at (b), in Fig. 390 ; 

 but more distinctly in Fig. 392, which is drawn 

 on a somewhat larger scale, and in which as 

 before (d) is the ear-drum ; (p) the promontory, 

 (o), the fenestra ovalis ; and (r) the fenestra 

 rotunda. These bones, which may be called 

 the tympanic ossicula, are four in number, and 

 are represented, enlarged to twice the natural 

 size, in Fig. 393. The names they have received 

 are more descriptive of their shape than of their 

 office. The first is the malleus, or hammer (m) ; 

 and its long handle (h) is affixed to the centre of 

 the ear-drum : the second is the incus, or anvil 

 (i) ; the third, which is the smallest in the body, 

 being about the size of a millet seed, is the orbi- 

 cular bone (o)* ; and the last is the stapes, or 

 stirrup (s), the base of which is applied to the 

 membrane of the fenestra ovalis. These bones 

 are regularly articulated together, with all the 

 ordinary apparatus of joints, and are moved by 

 small muscles provided for that purpose. Their 

 office is apparently to transmit the vibrations of 

 the ear-drum to the membrane of the fenestra 

 ovalis, and probably, at the same time, to in- 

 crease their force. 



* Blumenbach, and other anatomists, consider this as not 

 being a separate bone, but only a process of the incus ; a view 

 of the subject which is supported by the observations of Mr. 

 Shrapnell, detailed in the Medical Gazette, xii, 172. 



