GENERAL ANATOMY OF MUCOUS MEMBRANES. 63 



General Anatomy of Mucous Membranes. 



— The mucous membranes form the same sort of lining or 

 tegumentary covering to all the cavities of the body that the 

 skin does to the exterior ; and the two are continued insensibly 

 into one another at the orifices by which these cavities open 

 upon the surface. Hence the two are frequently spoken of as 

 the internal and external tegumentary systems. The first 

 general and satisfactory account of the mucous membranes we 

 owe to Bichat. He divided the whole class of mucous mem- 

 branes into two great divisions, the gastro-pulmonary , and 

 the genito-urinary. The gastro-pulmonary commences from 

 the mouth and nose, and from the eyes through the lachrymal 

 passages ; covers the nasal, buccal and pharyngeal cavities, and 

 is prolonged into the salivary ducts, the Eustachian tube, the 

 aerial passages and the whole length of the alimentary canal, 

 as well as the various secretory ducts which open into the 

 latter. 



— The genito-urinary lines the urethra, bladder, ureters, (and 

 pelvis of the kidneys in both sexes,) as well as the vagina, 

 uterus, and Fallopian tubes of the female where it opens 

 through the peritoneum into the cavity of the abdomen. In 

 the male it is prolonged from the bladder into the ducts of the 

 prostate, the vesiculae seminales, and the vas deferens, to the 

 termination of the last in the seminiferous ducts of the testicle. 

 Beneath the mucous membrane is a layer of cellular tissue 

 formerly called the nervous coat from its whiteness, which is 

 never found to contain any adipose matter, and is rarely infiltrat- 

 ed with serum. This connects the membrane in general to a 

 muscular plane below, as in the alimentary canal ; sometimes to 

 a contractile fibrous tissue as in many of the excretory ducts; 

 and occasionally to the periosteum, as in the nasal cavities. It 

 serves, as a basis to the mucous membrane, a sort of chorion or 

 dermis analogous to that of the skin, but which is in general 

 much more delicate, soft and spongy in its character ; an appear- 

 ance which the skin itself presents in many of the inferior ani- 

 mals and in very young foetuses. It varies in its thickness in 

 different parts of the body. It will be found to diminish 



