Section 58. the Outer Layer of the Skin (the Epidermis), the Inmost

lining of the alimentary canal, the lining of the body cavity, and the inner linings of blood-vessels, glands, and various ducts constitute our first division. The general name for such tissues is epithelium. When the cells are more or less flattened, they form squamous epithelium (Figure VI.) such as we find lining the inside of a man's cheek (from which the cells sq.ep. were taken) or covering the mesentery of various types-- sq.end. are from the mesentery (Section 16) of a frog. A short cylindroidal form of cell makes up columnar epithelium, seen typically in the cells covering the villi of the duodenum (Figure V.). This epithelium of the villi has the outer border curiously striated, and this is usually spoken of as leading towards "ciliated" epithelium, to be described immediately. The epithelium of the epididermis is stratified-- that is to say, has many thicknesses of cells; the deeper layers are alive and dividing (stratum mucosum), while the more superficial are increasingly flattened and drier as the surface is approached (stratum corneum) and are continually being rubbed off and replaced from below.