426 TPIE SENSORIAL FUNCTIONS. 



drum, at one end, and with the fenestra ovahs 

 at the other, there extends a chain of very 

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

 but more distinctly at m, i, s, in Fig. 393, which 

 is drawn on a somewhat larger scale, and in 

 which, as before, p is the promontory ; 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. 392. 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 orbicular 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 regu- 

 larly 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 increase 

 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. 



