. Animal physiology. Physiology, Comparative; Physiology, Comparative. 38 STRUCTURE OF MUCOUS MEMBRANE. projections, and also a number of minute pits. These projec- tions sometimes have the form of long folds ; in other instances they are narrow filaments, crowded together so as almost to re- semble the pile of velvet. In either case, the absorbent surface is vastly increased ; but chiefly so by these filaments, which are termed villi, and act as so many little rootlets. On the other hand, it is in the pits or follicles that the production of the fluid, which is to be separated or secreted fro
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 38 STRUCTURE OF MUCOUS MEMBRANE. projections, and also a number of minute pits. These projec- tions sometimes have the form of long folds ; in other instances they are narrow filaments, crowded together so as almost to re- semble the pile of velvet. In either case, the absorbent surface is vastly increased ; but chiefly so by these filaments, which are termed villi, and act as so many little rootlets. On the other hand, it is in the pits or follicles that the production of the fluid, which is to be separated or secreted from the blood, chiefly takes place. 39. The whole surface of every mucous membrane, whether simple or involuted, is usually covered with cells, resembling those of the epidermis, but never dried up into scales; and the layer formed by these cells, which sometimes adhere into a continuous membrane, whilst in other instances they readily separate from each other, is called the epithelium. This epithelium is frequently being cast off, like the epidermis; especially from the parts that are most concerned in secretion: and it is as continually being replaced, by the development of new cells from germs contained in the basement membrane, at the expense of fluid that transudes it from the blood-vessels copiously distributed beneath. Not only are the flat ex- panded surfaces of the mucous mem- brane covered with epithelium cells, but the villi also are sheathed by them; and the secreting follicles are lined by the same. It would appear, how- ever, that the epi- thelium cells of the have the pro-. Fig. 2. Diagram representing the Mucous Membrane of the Intestinal Canal ; A, in the intervals of digestion; B, tectlOfl of their deli- during digestion; a, a, absorbent vessels; b, b, basement membrane; c, c, epithelium cells; d, d, absorbent cells of villus; e, e, secreting cells of follicle. cate surface for their chief purpose; and. Please note that these images are extracted from scanned pa
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