

THE MIDDLE EAR. '59 



resembling those of the rest of the membrane lining the 

 tympanic cavity are only sparsely scattered, but are invested 

 by sheaths lying immediately beneath the epithelium. If the 

 epithelium be stripped off from the subjacent very thin layer of 

 connective tissue, an adenoid plexus appears, which in certain 

 regions is very compact, though large openings occur between 

 the groups. The openings lead into funnel-shaped or spheroidal 

 cavities, which again intercommunicate by spaces in the tissue, 

 and are finally continuous with tubes of various width. These 



Fig. 286. 



Fig. 286. Mucous membrane of the bulla ossea of the Dog. 

 Spaces are visible in the tissue, which at a and 6 are continuous 

 with lymphatics ; c, bloodvessels filled with gelatine. The pre- 

 paration was stained with chloride of gold. 



cavities are traversed by a fine plexus, and are lined by a very 

 delicate epithelium. They may either be empty or filled with 

 lymph corpuscles. They almost invariably contain fat drops 

 of. various size, which more or less run together. After macera- 

 tion in a solution of perosmic acid, these last become black, and 

 then sharply define the course of the tubes and the situation 

 of the cavities. I have, however, also seen fat drops in the 

 veins. However full the bloodvessels may become in con- 

 sequence of injections made from the aorta, the fluid never 

 penetrates into these cavities and tubes. This circumstance, as 



