Most of the muscles are spindle shaped, tapering at the ends. The tough tissue, which has been described as binding the strands together, forms at the ends into heavy tendons. Although, as you know, the muscle is soft and each strand would stand little pulling, when the minute contraction of each cell is multiplied by millions the resulting power is something.
The tendon ends are practically welded into the bones. The end attached to the bone which it does not move is called the origin. The other end where the bone moves a great deal is the insertion. The example best known to all of you is the calf of the leg with the origin on the bones at the knee and the long tendo Achilles, or heel tendon, running down some six inches to its insertion on the os calsis. You people must be lenient with us if we occasionally use our own favorite terms. Never have I heard a professional reference to a broken heel bone; it was always a fractured os calsis.
The tendo Achilles pulls the heel up, thereby causing the ankle to bend and the toe to go down. Feel it just above the heel, so that you may realize how heavy and powerful it is and how it gradually merges into the muscles at the bulge of the calf. How convenient for the grip of the mother of Achilles as she picked him up to dip him in the Styx.
E pluribus unum, which is engraved on our United States currency, is surely the motto of our muscles. I have told just above how the myriad cells of a muscle each adds its mite to form the might of a tendon. At least two muscles in the calf pull on the Achilles tendon; and the triceps on the back of the arm starts as three, merging into one. In fact, no one muscle ever works alone; always some others are either pulling with it or steadying it. Watch an athlete striving to win a hundred-yard dash. Every muscle in his body is cooperating, even to the muscles of expression in his face and even the muscles connected with the alimentary canal may take part.
As an illustration of the combined power of the soft muscle cells, I can tell you that they have been known to tear the great Achilles tendon in half. A fractured patella, or kneecap, is not uncommon and rarely does it result from a blow but from a spasmodic pull by the muscles on the front of the thigh. One of the last cases I handled was that of a delicate little woman of sixty-eight who missed her step from the curb to the street, and whose muscles gave such a jerk that she broke her kneecap.
These spindle-shaped muscles of the limbs are so designed that their bulk may be up out of the way, only slender tendons going to the hands and feet where trimness and unobstructed motion are desired. At the thighs, buttocks, and back, strength and disposition of weight close to the center of gravity are important and the muscles become more massive and ponderous at these parts. Also they are fused together so that it is difficult to say where one leaves off and another begins. But the nerve supply will tell the anatomist because as Dr. Herbert E. Walter so well expresses it: "A nerve once assigned to do duty with a muscle follows it through all its vicissitudes, just as a faithful dog, trotting behind its master, always serves to identify him, regardless of the different costumes or disguises which the master assumes."
A striking example of this fusion is the diaphragm, the great, flat, dome-shaped muscle which separates the abdomen from the chest cavity, and with which we do our best breathing, "belly breathing." The diaphragm originates in the neck; the phrenic nerve which controls it comes off from the spine not far from the skull and runs through the chest cavity. Some years ago it was customary to rest a tuberculous lung by temporarily paralyzing the diaphragm on that side. This was done by making a little incision in the neck just above the collarbone, picking up the nerve and crushing it. Later the injured nerve fibers would grow again and the diaphragm would become active.
Muscles under normal conditions always have some tonus. This means that they are never completely flabby but are kept on a slight amount of tension. Therefore they are always guarding and exerting some control over that part of the body they govern and are on the qui vive to move it if necessary. This tonus is bad, however, if exaggerated. A continuous tightening of the muscles is very exhausting. Athletes in the best of trim can make their muscles hard as iron, they also have more than average ability to relax them. Muscles at their highest efficiency also have to be handled with the greatest care. My poor arm now can throw a ball as well on the first try as on the tenth or twentieth; none of them good. A big league pitcher starts with a very short throw and takes fifteen minutes to warm up.