on the Membrana Tympani. g 



connecting the membrana tympani with another membrane 

 lining the foramen ovale, which opens into the vestibulum, a 

 more internal part of the organ of hearing. 



The bones are, the malleus, which is united to the membrana 

 tympani by a portion of its handle, and to the second bone or 

 incus by its head. The incus, which is connected to the mal- 

 leus by a capsular ligament, forming a regular joint, the sur- 

 faces of the bones being covered with cartilage, but they have 

 only a tremulous motion on one another. The incus is also 

 attached to the side of the cavity of the tympanum, where the 

 mastoid cells open, by a ligament on which it moves back- 

 wards and forwards : it is united by its long process to the 

 orbicular bone, which is the smallest in the body, and connects 

 the incus to the fourth bone or stapes, which has its base ap- 

 plied to the foramen ovale, or opening leading into the cavity of 

 the vestibulum. 



The cavity of the tympanum, in which these bones are si- 

 tuated, communicates with the external air by means of the 

 Eustachian tube, so that there is always air behind the mem- 

 brana tympani. 



The malleus has three muscles, by which it is moved; one 

 of them is called the tensor, from its pulling the malleus in- 

 wards, and tightening the membrana tympani : the other two 

 act in an opposite direction, and relax the membrane ; the lar- 

 gest of these is called the obliquus, and is the antagonist of the 

 tensor muscle ; the other is very small, and is called the laxator. 



The stapes has one muscle, which acts upon it by bringing 

 its basis closer to the foramen ovale. 



The vestibulum, which is completely separated from the 

 tympanum, by the membrane that lines the foramen ovale, com- 



mdccc C 



