MUCUS. 47 



with columnar, or conoidal epithelium. All of the mucous 

 membranes line cavities or tubes communicating with the 

 exterior by the different openings in the body. 



The following are the principal situations in which the 

 first variety of mucous membranes, covered with pavement- 

 epithelium, are found : The mouth, the lower part of the 

 pharynx, the oesophagus, the conjunctiva, the female ure- 

 thra, and the vagina. In these situations the membrane is 

 composed of a chorion made up of inelastic and elastic fibrous 

 tissue, a few fibro-plastic elements, with capillaries, lym- 

 phatics, and nerves. The elastic fibres are small and quite 

 abundant. The membrane itself is loosely united to the 

 subjacent parts by areolar tissue. The chorion is provided 

 with vascular papilla, more or less marked ; but in all situ- 

 ations, except in the pharynx, the epithelial covering fills up 

 the spaces between these papillse, so that the membrane pre- 

 sents a smooth surface. Between the chorion and the 

 epithelium, is an amorphous basement-membrane. The mu- 

 cous glands open upon the surface of the membrane by their 

 ducts, but the glandular structure is situated in the submu- 

 cous areolar tissue. These glands have many of them been 

 described in connection with the mucous membrane of the 

 mouth, pharynx, and oesophagus. 1 They are generally sim- 

 ple racemose glands, presenting a collection of follicles ar- 

 ranged around the extremity of a single excretory duct, lined 

 or filled with rounded, nucleated epithelium. 



The pavement-epithelium covering these membranes ex- 

 ists generally in several layers, and presents great variety, 

 both in form and size. The most superficial layers are 

 of large size, flattened, and irregularly polygonal. The 

 deeper layers are smaller and more rounded. The size of 

 these cells is from g-^j- to -g-j-^ of an inch. The cells are 

 pale, slightly granular, and possess a small, ovoid nucleus, 

 with one or two nucleoli. 



The second variety of mucous membranes, covered with 



2 See vol. ii., Digestion, p. 166. 



