THE MIDDLE EAR. 



367 



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 external 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, which commu- 

 "nicate freely with each other. The nerves supplying the tympanic mem- 

 brane accompany, for the most part, the blood-vessels and, in addition to 

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



The auditory ossicles are three small bones that form a chain 

 extending across the upper part of the tympanum from the tympanic mem- 

 brane to the labyrinth. The outermost of these, the malleus (hammer), is 



Epithelium of tympanic 

 surface 



Mucous membrane 



m 



Blood-vessels'^? >'*' / - 



Epidermis of drum-head 

 Subepidermal layer 

 External auditory canal 



Epidermis of canal 

 Corium of skin lining 



Epidermis passing onto 

 drum-head 





Bone 



Radial fibres of annulus 

 rosus 





FIG. 416. Section through attached margin of tympanic membrane, showing continuation of skin 

 and mucous membrane over its outer and inner' surfaces respectively. X 75- (Preparation by Dr. 

 Ralph Butler.) 



attached to the tympanic membrane; the innermost, the stapes (stirrup), is 

 fixed in the oval window, and between these two bones and connected with 

 both of them, lies the third link in the chain, the incus (anvil). Their sur- 

 faces of contact are covered with articular cartilage and enclosed to form 

 miniature true joints, provided with fibrous capsular ligaments and synovial 

 membranes. The bones do not lie exposed within the tympanic space, but 

 are invested with folds of the general mucous membrane lining the cavity. 



The Eustachian Tube. The Eustachian tube, or tuba auditiva, is a 

 canal, partly bony and partly cartilaginous, extending from the lateral wall of 

 the naso-pharynx backwards, upwards, and outwards to the anterior part of the 

 tympanum. In the adult it measures about 37 mm. in length, of which approx- 

 imately the upper third (tympanic portion) belongs to the bony division, 

 whilst the remainder is contributed by the cartilaginous division of the tube. 



