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 ends of the muscles are composed almost wholly of it. If every other tissue were removed, the connective tissue would still give a perfect model of all the organs. How abundant this tissue is in the skin may be known from the fact that leather consists entirely of it.

Fatty (Adipose) Tissue.—Fatty tissue is formed by the deposit of oil in connective tissue cells (see Fig. 14). Fat is held in meshes of connective tissue fibers. That fatty tissue consists not alone of fat, but of fibers also, is shown when hog fat is rendered into lard, certain tough parts called "cracklings" being left. What is the difference between beef fat and tallow?

Five fat cells, held in bundles of connective tissue fibers.

a is a large oil drop; m, cell wall; nucleus (n) and protoplasm (p) have been pushed aside by oil drop (a).

Epithelial tissue consists of one or more layers of distinct cells packed close together (see Fig. 15). It contains no connective tissue or other fibers, and is the simplest of the tissues. Epithelial tissue forms the outer layer of the skin, called the epidermis, and the mucous membrane lining the interior of the body. It contains no blood vessels, the epithelial cells obtaining their nourishment from the watery portion of the blood which soaks through the