STRUCTURE OF THE EUSTACHIAN TUBE. 279 



is columnar and ciliated in some parts, but in others e.g. roof, promon- 

 tory, ossicles, and membrana tympani it is a pavement-epithelium. 



The membrana tympani is a thin membrane formed of fibrous 

 bundles which radiate from the umbo. Within the radial fibres are a 

 few annular bundles. Covering the fibrous membrane externally is a 

 thin layer continuous with the skin of the meatus; covering it internally 

 is another thin layer, derived from the mucous membrane of the 

 tympanic cavity. Blood-vessels and lymphatics are distributed to the 

 membrane chiefly in the cutaneous and mucous layers. 



The Eustachian tube is the canal leading from the tympanum to the 

 pharynx. It is formed of bone near the tympanum, but below, near 



FlG. 311. --SECTION ACROSS THE CARTILAGINOUS PAET OF THE EUSTACHIAN TUBE. 



(Riidinger.) 



1, 2, bent cartilaginous plate ; 3, muse, dilatator tubse ; to the left of 4, part of the attach- 

 ment of the levator palati muscle ; 5, tissue uniting the tube to the base of the skull ; 

 6 and 7, mucous glands ; 8, 10, fat ; 9 to 11, lumen of the tube ; 12, connective tissue on 

 the lateral aspect of the tube. 



the pharynx, it is bounded partly by a bent piece of cartilage (fig. 311, 

 1, 2), partly by fibrous tissue. The latter contains numerous mucous 

 glands (6, 7), which open into the tube, and on the outer side a band of 

 muscular tissue (3) which joins the tensor palati. The epithelium is 

 ciliated. 



