OF HEARING. 



73 



with the round nodule at the extremity of the long process 

 of the incus ; the base of the bone (3) is of the ri , g 

 same figure as the foramen ; the lateral walls 

 of the arch (2, 2) are connected by a mem- 

 brane, and surmounted by a small head (1), 

 which articulates with the os orbiculare. These 

 four bones, when united together, form a chain, as shown 

 in fig. 49, where the membrane of Fig. 49. 



the tympanum is seen at (1), and 

 a, h, c, (I, are the bones by which 

 the membrane of the tympanum 

 is connected with that of the fo- 

 ramen ovale, the handle of the mal- 

 leus being attached to the tympanum, 

 and the base of the stapes being ap- 

 plied to the vestibular membrane. 

 The motions of this chain are regu- 

 lated by four small muscles, three of 

 which are inserted into the malleus, an d 

 one is attached to the stapes. T. W. J 



150. The internal ear, which is also denominated the 

 labyrinth, is an irregular cavity formed in the most solid part 

 of the temporal bone, beyond the chamber of the middle ear } 

 from which it is separated by a bony partition, and per- 

 forated by two small holes, called, from their form, the round 

 and the oval apertures, the foramen rciundum and the fora- 

 men ovale, 

 /.(fig. 45). 

 The first 

 is closed 

 by a mem- 

 brane simi- 

 lar to that 

 of the tym- 

 panum, 

 while the 

 latter is 



closed by 



the stapes. %' ^0. Relative situation of the Tympanum and Labyrinth. 



[The relative position of the tympanum and labyrinth is 

 shown in figure 50. (1), is the tympanum, with its tubes 



