STRUCTURE OF THE EUSTACHIAN TUBE 



231 



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, 



FIG. 268. SECTION ACROSS THE CARTILAGINOUS PART OF THE EUSTACHIAN TUBE. 



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

 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. 



near the pharynx, it is bounded partly by a bent piece of cartilage 

 (fig. 268, i, 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 epithe- 

 lium is ciliated. 



