460 BONES OF THE EAR. MALLEUS. INCUS. 



Under the above mentioned foramen is a more striking 

 protuberance called the Pror&ontory, within which is a 'part of 

 the Cochlea, the anterior division of the Labyrinth. 



At the under and posterior part of the promontory is the 

 Foramen Rotundum (fenestra rotunda,) which opens into 

 the Cochlea. This foramen is smaller than the foramen ovale ; 



and in its recent state is covered by the membrane which lines 

 , J 



the tympanum. 



According to M. Ribes,* the membrane closing the fenes- 

 tra rotunda, is a secondary membrane of the tympanum, 

 formed of three layers ; viz. the lining membrane of the tym- 

 panum, the lining membrane of the cochlea, and between them 

 a peculiar middle membrane ; its structure being like the mem- 

 brane which closes the bottom of the meatus auditorius externus. 

 It is probable that a similar arrangement, exists at the 

 fenestra ovalis, upon which the stapes rests, though it has 

 not been satisfactorily demonstrated. The size of both these 

 fenestra, is greatly inferior to that of the membrana tym- 

 pani. 



Behind the foramen ovale is a protuberance with a perfora- 

 tion in it. This is called the Pyramid. It is excavated, and 

 contains the muscle of the stapes, which passes out through the 

 perforation. 



The Bones of the Ear. 



The four small bones in the cavity of the tympanum are 

 denominated Malleus, Incus, Orbiculare, and Stapes. (See fig. 

 202, p. 463.) 



The Malleus resembles a crooked club more than any of 

 the hammers now in use. It consists of an irregular roundish 

 head, a neck, and a long tapering body, called the Manubrium, 

 or handle. It has also two processes ; one arising from the 

 neck, which is long and slender, like a bony fibre, and, there- 

 fore, called Gracilis. The other, called Brevis, arises from the 

 upper end of the handle. The handle of the Malleus forms an 



* Memoire stir Quelques Parties de FOreille Interne. 



