MUCOUS MEMBRANES AND MUCUS. 317 



female urethra and the vagina. In these situations the membrane is com- 

 posed of a chorion made up of inelastic and elastic fibrous tissue, with capil- 

 laries, lymphatics and nerves. The elastic fibres are small and quite abun- 

 dant. The membrane itself is loosely united to the subjacent parts. The 

 chorion is provided with vascular papillae, more or less marked ; but in all 

 situations, except in the pharynx, the epithelial covering fills up the spaces 

 between these papillae, so that the membrane presents a smooth surface. 

 Between the chorion and the epithelium, is an amorphous basement-mem- 

 brane. The mucous glands open upon the surface of the membrane by their 

 ducts, but the glandular structure is situated in the submucous tissue. Certain 

 of these glands have been described in connection with the anatomy of the 

 mucous membrane of the mouth, pharynx and oesophagus. They generally 

 are simple racemose glands, presenting a collection of follicles arranged around 

 the extremity of a single excretory duct, and lined or filled with rounded, 

 nucleated epithelium. The squamous epithelium covering these membranes 

 exists 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 ^-gVo" * o~o f an i ncn (1 to 83 //,). The cells are pale and 

 slightly granular, each with a small, ovoid nucleus and one or two nucleoli. 



The second variety of mucous membranes, covered with columnar epi- 

 thelium, is found lining the alimentary canal below the cardiac orifice of the 

 stomach, the biliary passages, the excretory ducts of all the glands, the nasal 

 passages, the upper part of the pharynx, the uterus and Fallopian tubes, 

 the bronchia, the Eustachian tubes and the male urethra. In certain situ- 

 ations this variety of epithelium is provided on its free surface with little 

 hair-like processes called cilia. During life the cilia are in constant motion, 

 producing a current generally in the direction of the mucous orifices. Ciliated 

 epithelium is found throughout the nasal passages, beginning about three- 

 quarters of an inch (19*1 mm.) within the nose ; in the upper part of the 

 pharynx ; the posterior surface of the soft palate ; the Eustachian tube ; the 

 tympanic cavity ; the larynx, trachea, and bronchial tubes, until they become 

 less than -^ of an inch (O5 mm.) in diameter ; the neck and body of the 

 uterus; the Fallopian tubes; the internal surface of the eyelids; and the 

 ventricles of the brain. Mucous membranes of this variety are formed of a 

 chorion, a basement-membrane and epithelium. The chorion is composed of 

 inelastic and elastic fibres, a few non-striated muscular fibres, amorphous mat- 

 ter, blood-vessels, nerves and lymphatics. It is less dense and less elastic 

 than the chorion of the first variety and generally is more closely united to 

 the subjacent tissue. The surface of these membranes is generally smooth, 

 the only exception being the mucous membrane of the pyloric portion of the 

 stomach and the small intestines. These membranes are provided with fol- 

 licular glands, extending through their entire thickness and terminating in 

 rounded extremities, sometimes single and sometimes double, which rest upon 

 the submucous structure. Many of them are provided also with simple race- 

 mose glands, the ducts passing through the membrane, and the glandular 



22 



