Within the sarcolemma are minute fibrils and a semiliquid substance, called the _sarcoplasm_. At each end the cell tapers to a point from which the sarcolemma appears to continue as a fine thread, and this, by attaching itself to the inclosing sheath, holds the cell in place. Most of the muscle cells receive, at some portion of their length, the termination of a nerve fiber. This penetrates the sarcolemma and spreads out upon a kind of disk, having several nuclei, known as the _end plate_. *The "Muscle-organ."*—We must distinguish between the term "muscle" as applied to the muscular tissue and the term as applied to a working group of muscular tissue, which is an organ. In the muscle, or muscle-organ, is found a definite grouping of muscle fibers such as will enable a large number of them to act together in the production of the same movement. An examination of one of the striated muscles shows the individual fibers to lie parallel in small bundles, each bundle being surrounded by a thin layer of connective tissue. (See Practical Work.) These small bundles are bound into larger ones by thicker sheaths and these in turn may be bound into bundles of still larger size (Fig. 109). The sheaths surrounding the fiber bundles are connected with one another and also with the outer covering of the muscle, known as [Fig. 109] Fig. 109—*Diagram* of a section of a muscle, showing the perimysium and the bundles of fiber cells. [Fig. 110] Fig. 110—*A muscle-organ in position.* The tendons connect at one end with the bones and at the other end with the fiber cells and perimysium. (See text.) *The Perimysium.*—The plan of the muscle-organ is revealed through a study of the perimysium. This is not limited to the surface of the muscle, as the name suggests, but properly includes the sheaths that surround the bundles of fibers. Furthermore, the surface perimysium and that within the muscle are both continuous with the strong, white cords, called _tendons_, that connect the muscles with the bones. By uniting with the bone at one end and blending with the perimysium and fiber bundles at the other, the tendon forms a very secure attachment for the muscle. The perimysium and the tendon are thus the means through which the fiber cells in any muscle-organ are made to _pull together_ upon the same part of the body (Fig. 110).