388 NEUROLOGY, OR ANATOMY OF NERVOUS SYSTEM 



and separates it from the jugular fossa beneath and the carotid 

 canal in front. The outer wall is formed by the rnembrana 

 tympani and the ring of bone into which this is inserted, and 

 presents, just in front of the bony ring, the Glaserian fissure, 

 which lodges the processus gracilis of the malleus and trans- 

 mits some tympanic vessels; at the back part, the iter posterius 

 for the entrance of the chorda tympani, and the iter anterius, 

 anteriorly, for its exit. The former leads to the aquseductus 

 Fallopii, the latter to the canal of Huguier. 



FIG. 68 



Cartilage of 

 the pinna ' 



1'romont. 



Int. carol, a. 



Cartilage of tin rj-f. 

 auditory '<itiix 



Transverse section of external auditory meatus and tympanum. (Gegenbaur.) 



The membrana tympani is a thin membrane inserted into 

 a ring of bone at the bottom of the external canal, which is 

 grooved for its reception. It is ovoid in form and directed 

 obliquely downward and inward. On its inner surface is the 

 handle of the malleus, which extends from about the middle 

 of its roof to a little below its centre, covered by mucous mem- 

 brane where it is attached. This process draws the membrane 

 inward, making its outer surface concave and its inner convex. 

 Externally, the membrane is covered by skin, continuous 

 with that of the meatus; internally, with mucous membrane, 

 continuous with that of the tympanum; and between these 

 two is a fibrous layer, some of its fibers radiating from the 



