MUCOUS MEMBRANES AND MUCUS 279 



covering fills the spaces between the papillae, so that the membrane 

 presents a smooth surface. Between the chorion and the epithelium, 

 is an amorphous basement-membrane. The mucous glands open on 

 the surface of the membrane by their ducts; but the glandular struc- 

 ture 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 usually are simple 

 racemose glands, presenting a collection of follicles arranged around 

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

 nucleated epithelium. The squamous epithelium covering these mem- 

 branes usually exists in several layers and presents great variety, 

 both in form and size. This is called stratified epithelium. The most 

 superficial layers are of large size, flattened and irregularly polygonal. 

 The deeper layers are smaller and more rounded. The size of the cells 



i s 2"Fo to TTiro f an * nc h ( IO to ^3 /*) They 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 

 epithelium, is found lining the alimentary canal below the cardiac 

 opening 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 situations this variety of epithelium is pro- 

 vided on its free surface with little hair-like processes called cilia. Dur- 

 ing life the cilia are in constant motion, producing a current usually 

 in the direction of the mucous orifices. Ciliated epithelium is found 

 throughout the nasal passages, beginning about three-quarters of ' an 

 inch (19 millimeters) 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 (0.5 millimeter) 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 epithe- 

 lium. The chorion is composed of inelastic and elastic fibres, a few 

 non-striated muscular fibres, amorphous matter, bloodvessels, nerves 

 and lymphatics. It is less dense and less elastic than the chorion of 

 the first variety and is more closely united to the subjacent parts. The 

 surface of these membranes is smooth, the only exception being the 

 mucous membrane of the pyloric portion of the stomach and of the 

 small intestines. These membranes are provided with follicular glands, 

 extending through their entire thickness and terminating in rounded 

 extremities, sometimes single and sometimes double, which rest on 



