THE EAR. 



179 



rected backwards, and projects at the mastoid cells. Its long cru^'^ 

 has a hooked apex, which is bent backward, and in contact with a 

 small lenticular bone, called orhiculare^ which is often fused into 

 the incus. 



The stapes or stirrup has its base or foot-piece" fitting the fenestra 

 ovalis ; one of its sides is more curved than the other, and its head 

 is in contact with the orbiculare. 



The muscles moving these bones are the tensor tympanic arising 

 from the spinous process of the sphenoid and the Eustachian tube, 

 and passing through that canal above the Eustachian tube, to be in- 

 serted into the upper part of the handle of the malleus, which it 

 draws inward, and thus stretches the membrane of the tympanum. 

 The laxator tijni'pani arises from the spinous process of the sphenoid 

 bone, and passes through the glenoid fissure, to be inserted into the 

 processus gracilis of the malleus. There is sometimes another and 

 lesser laxator tympani. The stapedius arises from the interior of 

 the pyramid, and its tendon escapes from its summit, to be inserted 

 into the neck of the stapes. 



Fig. 157. 



The Internal ear, or labyrinth, consists of three parts, the vesti- 

 hide, (V,) the semicircular canals, and the cochlea.^ 



The vestibule is a small, three-corneredxavity, behind the internal 

 wall of the tympanum ; into it open the semicircular canals," by 

 five orifices behind, and the cochlea,^ by a single one in front.**= On 

 its outer wall is the fenestra ovalis, and on its inner, several nminute 

 holes, including the macula cribrosa, for the entrance of a portion of 



