520 THE AUDITORY APPARATUS 



bone. From its origin it passes backwards and laterally, above 

 the osseous part of the auditory tube. In the tympanic cavity 

 the tendon turns at right angles, round the extremity of the 

 processus cochleariformis (p. 512), and passes laterally, towards 

 the lateral wall of the tympanum, to its insertion into the upper 

 part of the medial surface of the manubrium of the malleus. 

 The tensor tympani receives its nerve of supply through the 

 otic ganglion from the mandibular division of the trigeminal 

 nerve. The name of the muscle indicates its action. 



Chorda Tympani Nerve. The chorda tympani, which 

 traverses the tympanic cavity in close relation to the upper 

 part of the membrana tympani, is described on p. 182. 



External meatus 



Tympanic antrum 



Temporal line 



Mastoid notch (O,T. 

 Digastric fossa) 



Styloid Air-cells in mastoid part 

 process of temporal bone 



FIG. 219. Dissection of the Tympanic Antrum and the mastoid part of 

 the temporal bone from the outer side. 



Tympanic Plexus. This has been described previously 

 on p. 220. 



Tuba Auditiva (O.T. Eustachian). The auditory tube is 

 the passage which places the tympanic cavity in communica- 

 tion with the pharynx. Through it air reaches the tympanic 

 cavity and antrum and the mastoid cells. It consists of an 

 osseous and a cartilaginous portion. The osseous portion is 

 about 12.5 mm. (half an inch] in length. It is widest at its 

 entrance into the tympanum, and narrowest at its other end. 

 The cartilaginous portion is about an inch in length, and has 

 been already described on p. 298. 



Dissection : Second Method. On the opposite side the bony 

 part of the external meatus, the tympanic antrum, and the 



