30 THE EXTERNAL AND MIDDLE EAR, BY J. KESSEL. 



few fat molecules and pigment granules are imbedded ; with 

 these are mingled hairs and epidermis scales from the lining of 

 the meatus, with particles of very various nature derived from 

 without. When accumulated in considerable quantity, and 

 allowed to remain for a long period in the meatus, the cerumen 

 becomes altered in colour, and in consequence of the evapora- 

 tion of its watery portion forms consistent masses, the so-called 

 ceruminous plugs. 



The larger arterial vessels run to the upper and posterior 

 wall of the auditory meatus, and from these a large branch is 

 given off, which is distributed to the membrana tympani. 



The principal nerve trunks that were previously found in 

 the cutis of the cartilaginous portion of the meatus break up 

 in the osseus meatus into numerous branches, so that at the 

 end of this passage the surface of expansion of the nerves, 

 as compared with the outer parts, is considerably increased, 

 which is in accordance with the great sensitiveness of these 

 parts. 



The membrana tympani is expanded like a septum between 

 the external auditory meatus and the tympanum. 



This membrane usually presents the form of an ellipse, the regula- 

 rity of which is broken by the Kivinian hiatus or gap, which is situated 

 anteriorly and to the upper part. The longer axis of this ellipsoid 

 extends from behind and above, downwards and forwards, the shorter 

 is directed from before and above, backwards and downwards. Cor- 

 responding to this, the diameter of the membrana tympani should be 

 measured in the direction of the axes of the ellipsoid, and not, as is 

 usually done, in the vertical and horizontal diameter. Different 

 values are obtained in the two cases ; in the former, when the longer 

 axis of the ellipsoid is measured, it amounts to 9*5 10 millimeters, 

 whilst the shorter is 8 millimeters ; in the other case, the horizontal 

 diameter is from 8 8'5, and the vertical 8'5 9 millimeters. 



The planes of attachment of the tympanic membranes of opposite 

 sides are inclined to one another ; their inclination is indicated by 

 angles opening above and posteriorly, the former divergence amount- 

 ing to 180 185, the latter having not as yet been satisfactorily 

 determined. The membrana tympani itself does not lie in the plane of 

 its attachment, but presents a curved surface, so that it forms a kind of 

 funnel, the apex of which is situated at the lower part of the handle 



