602 



THE NERVOUS SYSTEM. 



the rest, and has therefore received the name membrana flaccida. 

 It is called also ShrapneWs membrane. 



When a normal membrana tympani is viewed through an aural 

 speculum, there is seen a triangular spot or cone or pyramid of 

 light, whose apex is at the end of the manubrium or handle of the 

 malleus, and whose base is at the circumference. The membrane 

 is funnel-shaped, with the concavity toward the meatus, at the 

 apex being attached the tip of the manubrium, and at this point 

 on the outer surface is the umbo (Fig. 379). 



Tympanic Cavity (Fig. 378). In this cavity, which is situated 

 in the petrous portion of the temporal bone, are the chains of bones, 

 the ossicles, serving as a B 



means of communication 

 between the membrana 

 tympani and the internal 

 ear. It communicates 

 posteriorly with the mas- 

 toid antrum and the mas- 



FIG. 380. The ossicles of the 

 left ear, external view (enlarged) 

 (after Gray). 



FIG. 381. Malleus of the right side : A, 

 anterior face ; B, internal face ; 1, capitulum 

 or head of malleus ; 2, cervix or neck ; 3, 

 processus brevis; 4, processus gracilis; 5, 

 manubrium ; 6, grooved articular surface for 

 incus ; 7, tendon of musculus tensor tympani 

 (after Testut). 



toid cells, and anteriorly with the pharynx by means of the Eusta- 

 chian tube. Two openings, the fenestra ovalis and fenestra rotunda, 

 give it communication with the internal ear. The roof of the tym- 

 panic cavity, the tegmen, is a very thin plate of bone, the only struc- 

 ture separating this cavity from that in which lies the brain. It is 

 on account of this slight separation that inflammation of the middle 

 ear sometimes extends to the brain. The tympanic cavity is lined 

 by mucous membrane, which is covered with ciliated epithelium 

 except over the ossicles and the membrana tympani. 



Ossicles (Fig. 380). These are three in number : the malleus, 

 the incus, and the stapes. 



Malleus (Fig. 381). The malleus is about 18 mm. long, and 

 consists of head, neck, manubrium, processus gracilis, and processus 

 brevis. 



The head has a general surface for articulation with the incus. 



