MUCOUS MEMBRANE OF THE TYMPx\.XUM. 639 



rifvn fissure to the attachment of the short process of the incus posteriorly. The 

 tendon of the tensor tympani muscle passing from within to be inserted below that 

 line, pulls tlie handle of the malleus inwards (fig. 450. i*). while the laxator tympani 

 inserted above that line, by pulling the head of the bone inwards (/), moves the 

 handle outwards. The incus, moving along with the malleus. jDUshes the ctapes 

 inwards towards the internal ear when the membrana tympani is made tight, and 

 di-aws that bone in an opposite direction, when the membrana tj-mpani is relaxed. 

 In this movement the head of the stapes is slightly raised as well as jiressed in- 

 wards, and the upper margin of its base moves more than the lower. But the cavity 

 of the inner ear is full of liquid ; and its walls are iinyielding, except at the fenestra 

 rotunda ; when, therefore, the stapes is pushed inwards the secondary membrane 

 of the t;y'mpanum, which blocks up the fenestra rotunda, must be made tense by 

 pressure from within. The attachment of the handle of the malleus, however, 

 to the membrana tj-mpani allows greater freedom of movement to that process 

 than is allowed to the stapes by the ligaments of its base, and when the move- 

 ment of the stapes ceases, the malleus rotates on the head of the incus without 

 di-agging the stapes fui-ther fi-om the fenestra ovalis : and hence, probably, the 

 necessity of a moveable articulation between those bones. The action of the 

 stapedius muscle is ob^dously to draw the head of the staj^es backwards, in doing 

 which the hinder end of the base of that bone will be pressed against the 

 margin of the fenestra ovalis, while the fore pai-t vnil be withdi'awn from the 

 fenestra.* 



a?HE LINING MEMBRANE OF THE TYMPANUM. 



The mucous membrane of the tympanum is continuous with that of 

 the pharynx through the Eustachian tube, and is further prolonged 

 from the tympanum backwards into the mastoid cells. Two folds 

 which cross the breadth of the cavity descend from the part of the 

 membrane which lines the roof. The anterior fold turns round the 

 tendon of the tensor tympani muscle ; the posterior fold passes round 

 the stapes. The malleus and incus are invested by the lining of the 

 outer wall of the cavity. The mucous membrane which lines the 

 cartilaginous part of the Eustachian tube resembles much the mem- 

 brane of the pharynx, with which it is immediately continuous ; it is 

 thick and vascular, is covered by laminated epithelium surmounted by 

 vibratile cilia, and is provided with many simple mucous glands 

 Avhich pour out a thick secretion : in the osseous part of the tube, 

 however, this membrane becomes gradually thinner. In the tym- 

 panum and the mastoid cells the mucous membrane is paler, thinner^ 

 and less vascular, and secretes a less viscid, somewhat yellow fluid. 

 Between it and the periosteum is a more or less developed network of 

 fibrous bundles, which are here and there raised above the general 

 surface, causing corresponding projections of the mucous membrane. 

 Moreover, in various places on the interlacing bundles, peculiar 

 swellings occur of various sizes, which appear to be caused by 

 the super-addition of concentrically arranged fibres upon the smaller 

 bundles, and produce an appearance similar to that of miniature 

 Pacinian corpuscles (Politzer, Kessel). The epithelium in the tympanic 

 cavity is for the most part columnar and ciliated, but the roof, the pro- 

 montory, the ossicula, and the membrana, are covered with a simple 

 layer of iBattened, non-ciliated cells (v. Troeltsch). 



* For furtlier information with regard to the anatomical relations of the bones and 

 membranes, and the mode in which they act, see Helmholtz, Die Mechanik der Gelior- 

 kniichelchen iind des Trommelfells, Plliiger's Archiv, vol. i. ; also English Translation, 

 American edition. 



