THE MIDDLE EAR. 51 



The latter forms a fine plexus immediately beneath the 

 epithelium, supplying this last also with fibrils. 



6. THE MIDDLE EAR. 



The term middle ear includes (1) the tympanic cavity, 

 with the ossicula contained in it, and their muscles and 

 ligaments ; (2) the cells of the mastoid process ; and (3) the 

 Eustachian tube. 



THE TYMPANIC CAVITY. The bony walls of this cavity, the 

 structures found in it, as well as the inner surface of the mem- 

 brana tympani, are covered by mucous membrane, which is 

 continuous with that lining the Eustachian tube, and at the 

 same time passes through the antrum mastoideum into the cells 

 of the mastoid process. The mucous membrane of the tym- 

 panic cavity of Man is, speaking generally, composed of an 

 epithelium and a subjacent layer of connective tissue. 



The epithelium presents various forms. On the floor and 

 lower portion of the anterior, internal, and posterior walls of the 

 cavity it consists chiefly of ciliated columnar cells ; on the pro- 

 montory, the roof, the membrana tympani, and the ossicula, it 

 is tesselated (v. Troeltsch, 45). The transition of the former into 

 the latter is gradual, the ciliated columnar cells becoming lower, 

 and passing into tesselated ciliated epithelium, and finally into 

 non-ciliated pavement cells. If the columnar epithelium be 

 separated from the subjacent tissue, and an attempt be made 

 to isolate the cells, cup-cells are found resembling those of the 

 intestinal mucous membrane, together with columnar cells both 

 with and without nuclei, of which the non-nucleated possess 

 an extremely slender and often rod-shaped body, and a slender 

 brush of cilia which are often adherent to each other. Both 

 forms are continuous below with homogeneous strongly refrac- 

 tile fibres. They are sometimes forked at their lower extremity, 

 and are then in connection with two such fibres. In a speci- 

 men prepared by teazing, I have succeeded in isolating a cell 

 with two processes, of which one still remained in connection 

 with a fibre three times the length of the cell, which could be 

 traced beyond this for some distance into the connective tissue. 



B 2 



