TYMPANIC MUCOUS MEMBRANE 517 



of the aditus the canalis facialis descends along the posterior 

 border of the medial wall of the tympanum. 



The antero-posterior diameter of the tympanic antrum is 

 about 14 mm., the vertical diameter, about 9 mm., and the 

 transverse diameter, about 7 mm. 



Tympanic Mucous Membrane. The tympanum is lined, 

 throughout, with a thin mucous membrane which is continuous 

 with the mucous membrane of the pharynx, through the 

 auditory tube. As already mentioned, it forms the medial 

 layer of the membrana tympani, and it is prolonged posteriorly 

 into the tympanic antrum and mastoid air-cells. It covers 

 the ossicles also, and it invests the tendons of the stapedius 

 and tensor tympani muscles. 



Facet for Head 



incus | Processus 

 anterior 



Manubrium Manubrium 



A B 



FIG. 215. The Left Malleus. (Howden. ) 



A. Posterior aspect. B. Medial aspect. 



Ossicula Auditus. The auditory ossicles are the malleus, the incus, 

 and the stapes. 



The malleus presents a head, a neck, a manubrium, and two processes 

 termed the processus lateralis and the processus anterior. The head is 

 large and rounded. It is directed upwards, and lies above the level of the 

 membrana tympani, in the recessus epitympanicus, close to the roof and 

 the lateral wall of the tympanum (Figs. 209, 211). On its posterior aspect 

 there is a notch-like articular surface, for articulation with the body of the 

 incus. The manubrium is attached to the fibrous layer of the membrana 

 tympani. The processus lateralis (O.T. brevis} is a stunted projection 

 which springs from the root of the manubrium. It is directed laterally, and 

 abuts against the membrana tympani immediately below the membrana 

 flaccida. The processus anterior (O.T. gracilis} is a slender spicule of bone 

 which passes forwards and downwards into the petro-tym panic fissure. 

 It almost invariably breaks when the malleus is detached from the adult 

 skull, but it can be easily preserved in the skull of an infant. 



The incus is shaped somewhat like a prsemolar tooth in which the roots 

 are very divergent, It presents a body and a long and a short crus, The 

 ill 33 6 



