380 



THE SENSORIAL FUNCTIONS. 



leading into numerous cells, contained in the mas- 

 toid process of the temporal bone, and therefore 

 termed the mastoid cells: these cells are likewise 

 filled with air. The innermost side of the same 

 cavity, that is the side opposite to the ear-drum, 

 and which is shown in Fig. 391, is occupied by a 

 rounded eminence (p), of a triangular shape, 

 termed the promontory ; on each side of which 



there is an opening in the bone, closed, however, by 

 the membrane lining the whole internal surface of 

 the cavity. The opening (o), which is situated at 

 the upper edge of the promontory, is called the 

 fenestra ovalis, or oval window ; and that near the 

 under edge (r), is the fenestra roturida^ or round 

 window. 



Connected with the membrane of the ear-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 

 at M, I, s, in Fig. 393, which is drawn on a some- 

 what larger scale, and in which, as before, p is the 

 ])romontory ; and r the fenestra rotunda. These 

 bones, which may be called the tympanic ossicular 

 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 



