THE MIDDLE EAR. 



H95 



the malleus handle and at the periphery of the membrane. The veins are most numerous at the 

 handle of the malleus and periphery of the membrane and communicate with those of the exter- 

 nal meatus and tympanic cavity. 



The lymphatics are arranged similarly to the blood-vessels in two sets, one under the skin 

 and the other under the mucous membrane. They communicate freely with each other and 

 probably empty partly into the lymph-nodes situated over the mastoid process and in the 

 region of the tragus, and partly into the lymph-tracts of the Eustachian tube and thence event- 

 ually into the retropharyngeal and deep cervical nodes. 



FIG. 1253. 



Epithelium of tympanic 

 surface 



Circular fibres 

 Radial fibres- 



Mucous membrane 



Blood-vessels 



Epidermis of drum-head 

 Subepidermal layer 

 External auditory canal 



Epidermis of canal 



Corium of skin lining 

 canal 



. ' Epidermis passing onto 



drum-head 



O*' 



Bone 



Radial fibres of annulus 

 fibrosus 



Section through attached margin of tympanic membrane, showing continuation of skin and mucous membrane 

 over its outer and inner surfaces respectively. X 75- Drawn from preparation made by Dr. Ralph Butler. 



The nerves supplying the tympanic membrane are derived chiefly from the auriculo-tem- 

 poral branch of the trigemlnus, supplemented by twigs from the tympanic plexus and by the 

 auricular branch of the vagus. They accompany, for the most part, the blood-vessels and, in 

 addition to supplying the latter, form both a subcutaneous and a submucous plexus. 



The inner wall (paries labyrinthica) of the tympanic cavity separates it from 

 the internal ear. It presents for examination a number of conspicuous features. 



The promontory appears as a well-marked bulging of the inner wall near its 

 middle (Fig. 1254) and corresponds to the first turn of the cochlea. The branches 

 of the tympanic plexus are found in the mucous membrane covering it. At the 

 bottom of a niche, whose anterior border is formed by the lower posterior margin 

 of the promontory, lies the round window (fenestra cochlea). It is closed by 

 the secondary tympanic membrane (membrana tympani secundaria), which 

 separates the tympanic cavity from the scala tympani of the cochlea (Fig. 1259). 

 The membrane is attached in an obliquely placed groove, is slightly concave 

 toward the tympanum, and measures from 1.5-3 mm - m diameter. The oval 

 window (fenestra vestibuli) lies at the bottom of a depression, the fossula 

 vestibuli, in the upper back part of the inner wall, above the round window, and 

 leads into the vestibule. It is somewhat kidney-shaped, its upper border being 

 concave, its lower slightly convex. In the recent state the oval window is closed 

 by the foot-plate of the stapes and the ligament which connects the ossicle with 

 the sides of the window (Fig. 1260). The longest diameter of the latter is 

 about 3 mm. and its shortest 1.5 mm. Abov the oval window 'a well-marked 



