n. A case or covering, especially one which fits closely: as, the sheath of a sword. Compare scabbard.n. Any somewhat similar covering.n. In zoology, some sheathing, enveloping, or covering part.n. () The preputlal sheath into which the penis is retracted in many animals, as the horse, bull, dog, etc. This sheath corresponds in the main with the foreskin of man, and is often called prepuce.n. An elytron, wing-cover, or wing-case of an insect.n. The horny covering of the bill or feet of a bird; especially, a sort of false cere of some birds, as the sheathbills, jagers, etc. See cuts under puffin.n. The lorica or test which envelops many infusorians or other protozoans, some rotifers, etc.n. The fold of skin into which the claws of a cat or other feline may be retracted.n. In anatomy, specifically, a membrane, fascia, or other sheet or layer of condensed connective tissue which closely invests a part or organ, and serves to bind it down or hold it in place. Such sheaths may be cylindrical, as when investing a nerve or blood-vessel and extending in its course; or flat and expansive, as when binding down muscles. A layer of deep fascia commonly forms a continuous sheath of all the muscles of a limb, as notably in the case of the fascia lata, which envelops the thigh, and is made tense by a special muscle (the tensor fasciæ latæ). See fascia, 7.n. A structure of loose stones for confining a river within its banks.n. The sheath of a leaf.n. Specifically— The membranous toothed girdle which surrounds each node of an Equisetum, corresponding to the foliage of the higher orders of plants. See cut under Equisetum.n. The outer leaf becomes thickened about the middle of the internode, inclosing a nucleus.Same as sheathe.n. In old plows, the bar connecting the beam and sole in front: so called as sheathing the edge of the mold-board. It corresponds to the standard and in part to the shin (see shin, 8) of a modern plow. See plow, 1.n. The white substance of Schwann which surrounds the axis-cylinder in a nerve-fibril.
