274 SPECIAL ANATOMY. 



auditory passage ; its internal surface upwards and inwards into the 

 cavity of the tympanum, and presents in the centre an elevation 

 where the handle of the Malleus draws it inwards (on the external 

 surface a funnel-shaped excavation). Its margin lies in the sukus 

 tympani ; close to that, at the superior posterior part of the mem- 

 hrana tympani, the short process of the malleus presses the last 

 outwards (umbo) ; at the posterior extremity of the horizontal 

 diameter it is perforated by the Chorda tympani. 



The membrana tympani consists of three laminfe ; the external 

 is the sack-like extremity of the skin (cutis or epidermis) of the 

 auditory passage ; the internal is a prolongation of the thin mucous 

 membrane of the tympanic cavity ; the central the proper tympanic 

 membrane, is very strong, fibrous (according to Ev. Home muscular), 

 its fibres converge from the circumference towards the centre. The 

 vessels appear to belong exclusively to the internal lamina. They 

 form a close rete, circul. vasor. major and minor (as in the Iris). 



Art. tympanica superior (from stylomastoid, s. auricular, poster.") and inferior 

 (from maxill. interna or externa). 



Nerves: auricul. anterior (trigemmi.) 



The membrana tympani is strained and vibrates feebly under 

 strong, but is relaxed and vihrates strongly under feeble impres- 

 sions produced by the undulations of sound. 



B. The central part of the Ear. 



509. 1. The cavity of the tympanum, tympanum, cavitas 

 tympani, 



an irregular, oblong, (four and a half lines) narrow (two lines) ca- 

 vity, situated at the anterior part of the basis oss. petrosi, between 

 the external auditory canal and the labyrinth. Anteriorly it is in 

 connexion by the tuba Eustachii with the Pharynx, behind and 

 above, where it is more spacious, with the cells ofproc. Mastoideus. 

 Its external wall is formed by the osseous plate in which the 

 memb. tympani is strained as well as by this itself; it is bounded 

 before byfissura Glaseri (for chorda tympani, art. tympan. infer. 

 and lig. mallei anterius). The internal wall [fundus] lies oppo- 

 site to the memb. tympani, and presents : 



a. Fenestra ovalis s. vestibuli, an oblong opening, directed obliquely down- 

 wards and forwards (H line long), at the superior part of the internal wall, 

 lying in a depression, bounded above by canal. Fallopice, below by promonto- 

 rium, is closed by the footpiece of the Stapes and a thin membrane. Under it, 



b. Promontorium s. tuber cochlea, an elevation which corresponds to one 



