_Muscles which tend to keep the body from falling backward._

D, muscles of the front of the leg; E, of the front of the thigh; F, of the front of the abdomen; G, of the front of the neck.

76. Important Muscles. There are scores of tiny muscles about the head, face, and eyes, which, by their alternate contractions and relaxations, impart to the countenance those expressions which reflect the feelings and pa.s.sions of the individual. Two important muscles, the temporal, near the temples, and the ma.s.seter, or chewing muscle, are the chief agents in moving the lower jaw. They are very large in the lion, tiger, and other flesh-eating animals. On the inner side of each cheek is the buccinator, or trumpeter's muscle, which is largely developed in those who play on wind instruments. Easily seen and felt under the skin in thin persons, on turning the head to one side, is the sterno-cleido-mastoid muscle, which pa.s.ses obliquely down on each side of the neck to the collar bone--prominent in sculpture and painting.

The chest is supplied with numerous muscles which move the ribs up and down in the act of breathing. A great, fan-shaped muscle, called the pectoralis major, lies on the chest. It extends from the chest to the arm and helps draw the arm inward and forward. The arm is raised from the side by a large triangular muscle on the shoulder, the deltoid, so called from its resemblance to the Greek letter delta, ?. The biceps, or two-headed muscle, forms a large part of the fleshy ma.s.s in front of the arm. Its use is to bend the forearm on the arm, an act familiarly known as "trying your muscle." Its direct antagonist is the three-headed muscle called the triceps. It forms the fleshy ma.s.s on the back of the arm, its use being to draw the flexed forearm into a right line.

On the back and outside of the forearm are the extensors, which straighten the wrist, the hand, and the fingers. On the front and inside of the forearm are the flexors, which bend the hand, the wrist, and the fingers. If these muscles are worked vigorously, their tendons can be readily seen and felt under the skin. At the back of the shoulder a large, spread-out muscle pa.s.ses upward from the back to the humerus. From its wide expanse on the back it is known as the latissimus dorsi (broadest of the back). When in action it draws the arm downward and backward, or, if one hangs by the hands, it helps to raise the body. It is familiarly known as the "climbing muscle."

[Ill.u.s.tration: Fig. 37.--A Few of the Important Muscles of the Back.]

Pa.s.sing to the lower extremity, the thigh muscles are the largest and the most powerful in the body. In front a great, four-headed muscle, quadriceps extensor, unites into a single tendon in which the knee-cap is set, and serves to straighten the knee, or when rising from a sitting posture helps elevate the body. On the back of the thigh are several large muscles which bend the knee, and whose tendons, known as the "hamstrings," are readily felt just behind the knee. On the back of the leg the most important muscles, forming what is known as the calf, are the gastrocnemius and the soleus. The first forms the largest part of the calf. The soleus, so named from resembling a sole-fish, is a muscle of broad, flattened shape, lying beneath the gastrocnemius. The tendons of these two muscles unite to form the tendon of Achilles, as that hero is said to have been invulnerable except at this point. The muscles of the calf have great power, and are constantly called into use in walking, cycling, dancing, and leaping.

77. The Effect of Alcoholic Drinks upon the Muscles. It is found that a man can do more work without alcohol than with it. After taking it there may be a momentary increase of activity, but this lasts only ten or fifteen minutes at the most. It is followed by a rapid reduction of power that more than outweighs the momentary gain, while the quality of the work is decidedly impaired from the time the alcohol is taken.

Even in the case of hard work that must be speedily done, alcohol does not help, but hinders its execution. The tired man who does not understand the effects of alcohol often supposes that it increases his strength, when in fact it only deadens his sense of fatigue by paralyzing his nerves. When put to the test he is surprised at his self-deception.

Full intoxication produces, by its peculiar depression of the brain and nervous system, an artificial and temporary paralysis of the muscles, as is obvious in the pitifully helpless condition of a man fully intoxicated.

But even partial approach to intoxication involves its proportionate impairment of nervous integrity, and therefore just so much diminution of muscular force. All athletes recognize this fact, as while training for a contest, rigid abstinence is the rule, both from liquors and tobacco. This muscular weakness is shown also in the unsteady hand, the trembling limbs of the inebriate, his thick speech, wandering eye, and lolling head.

78. Destructive Effect of Alcoholic Liquors upon Muscular Tissue.

Alcoholic liquors r.e.t.a.r.d the natural chemical changes so essential to good health, by which is meant the oxidation of the nutritious elements of food. Careful demonstration has proved also that the amount of carbon dioxide escaping from the lungs of intoxicated persons is from thirty to fifty per cent less than normal. This shut-in carbon stifles the nervous energy, and cuts off the power that controls muscular force. This lost force is in close ratio to the retained carbon: so much perverted chemical change, so much loss of muscular power. Not only the strength but the fine delicacy of muscular action is lost, the power of nice control of the hand and fingers, as in neat penmanship, or the use of musical instruments.

To this perverted chemical action is also due the fatty degeneration so common in inebriates, affecting the muscles, the heart, and the liver.

These organs are encroached upon by globules of fat (a hydrocarbon), which, while very good in their proper place and quant.i.ty, become a source of disorder and even of death when they abnormally invade vital structures. Other poisons, as phosphorus, produce this fatty decay more rapidly; but alcohol causes it in a much more general way.

This is proved by the microscope, which plainly shows the condition mentioned, and the difference between the healthy tissues and those thus diseased.

[Ill.u.s.tration: Fig. 38.--Princ.i.p.al Muscles on the Left Side of Neck.

A, buccinator; B, ma.s.seter; C, depressor anguli oris; D, anterior portion of the digastric; E, mylo-hyoid; F, tendon of the digastric; G, sterno-hyoid; H, sterno-thyroid; K, omo-hyoid; L, sternal origin of sterno-cleido-mastoid muscle; M, superior fibers of deltoid; N, posterior scalenus; O, clavicular origin of sterno-cleido-mastoid; P, sterno-cleido-mastoid; R, trapezius; S, anterior constrictor; T, splenius capitis; V, stylo-hyoid; W, posterior portion of the digastric; X, fasciculi of ear muscles; Z, occipital.

[NOTE. It was proposed during the Civil War to give each soldier in a certain army one gill of whiskey a day, because of great hardship and exposure. The eminent surgeon, Dr. Frank H. Hamilton of New York, thus expressed his views of the question: "It is earnestly desired that no such experiment will ever be repeated in the armies of the United States. In our own mind, the conviction is established, by the experience and observation of a life, that the regular routine employment of alcoholic stimulants by man in health is never, under any circ.u.mstances, useful. We make no exceptions in favor of cold or heat or rain."

"It seems to me to follow from these Arctic experiences that the regular use of spirits, even in moderation, under conditions of great physical hardship, continued and exhausting labor, or exposure to severe cold cannot be too strongly deprecated."

A. W. Greely, retired Brigadier General, U.S.A., and formerly leader of the Greely Expedition.]

79. Effect of Tobacco on the Muscles. That other prominent narcotic, tobacco, impairs the energy of the muscles somewhat as alcohol does, by its paralyzing effect upon the nervous system. As all muscular action depends on the integrity of the nervous system, whatever lays its deadening hand upon that, saps the vigor and growth of the entire frame, dwarfs the body, and r.e.t.a.r.ds mental development. This applies especially to the young, in the growing age between twelve or fourteen and twenty, the very time when the healthy body is being well knit and compacted.

Hence many public schools, as well as our national naval and military academies, rigidly prohibit the use of tobacco by their pupils. So also young men in athletic training are strictly forbidden to use it.[12] This loss of muscular vigor is shown by the unsteady condition of the muscles, the trembling hand, and the inability to do with precision and accuracy any fine work, as in drawing or nice penmanship.

Additional Experiments.

Experiment 23. _ To examine the minute structure of voluntary muscular fiber._ Tease, with two needles set in small handles, a bit of raw, lean meat, on a slip of gla.s.s, in a little water. Continue until the pieces are almost invisible to the naked eye.

Experiment 24. Place a clean, dry cover-gla.s.s of about the width of the slip, over the water containing the torn fragments. Absorb the excess of moisture at the edge of the cover, by pressing a bit of blotting-paper against it for a moment. Place it on the stage of a microscope and examine with highest obtainable power, by light reflected upward from the mirror beneath the stage. Note the apparent size of the finest fibers; the striation of the fibers, or their markings, consisting of alternate dim and bright cross bands. Note the arrangement of the fibers in bundles, each thread running parallel with its neighbor.

Experiment 25. _To examine the minute structure of involuntary muscular fiber, a tendon, or a ligament._ Obtain a very small portion of the muscular coat of a cow's or a pig's stomach. Put it to soak in a solution of one dram of bichromate of potash in a pint of water. Take out a morsel on the slip of gla.s.s, and tease as directed for the voluntary muscle. Examine with a high power of the microscope and note: (1) the isolated cells, long and spindle-shaped, that they are much flattened; (2) the arrangement of the cells, or fibers, in sheets, or layers, from the torn ends of which they project like palisades.

Experiment 26. Tease out a small portion of the tendon or ligament in water, and examine with a gla.s.s of high power. Note the large fibers in the ligament, which branch and interlace.

Experiment 27. With the head slightly bent forwards, grasp between the fingers of the right hand the edge of the left sterno-cleido-mastoid, just above the collar bone. Raise the head and turn it from left to right, and the action of this important muscle is readily seen and felt. In some persons it stands out in bold relief.

Experiment 28. The tendons which bound the s.p.a.ce (popliteal) behind the knee can be distinctly felt when the muscles which bend the knee are in action. On the outer side note the tendons of the biceps of the leg, running down to the head of the fibula. On the inside we feel three tendons of important muscles on the back of the thigh which flex the leg upon the thigh.

Experiment 29. _To show the ligamentous action of the muscles._ Standing with the back fixed against a wall to steady the pelvis, the knee can be flexed so as to almost touch the abdomen. Take the same position and keep the knee rigid. When the heel has been but slightly raised a sharp pain in the back of the thigh follows any effort to carry it higher. Flexion of the leg to a right angle, increases the distance from the lines of insertion on the pelvic bones to the tuberosities of the tibia by two or three inches--an amount of stretching these muscle cannot undergo. Hence the knee must be flexed in flexion of the hip.

Experiment 30. A similar experiment may be tried at the wrist. Flex the wrist with the fingers extended, and again with the fingers in the fist. The first movement can be carried to 90, the second only to 30, or in some persons up to 60. Making a fist had already stretched the extensor muscles of the arm, and they can be stretched but little farther. Hence, needless pain will be avoided by working a stiff wrist with the parts loose, or the fingers extended, and not with a clenched fist.

Review a.n.a.lysis: Important Muscles.

Location.

Name. Chief Function.

Head and Neck.

Occipito-frontalis. moves scalp and raises eye brow.

Orbicularis palpebrarum. shuts the eyes.

Levator palpebrarum. opens the eyes.

Temporal. raise the lower jaw.

Ma.s.seter. " " " "

Sterno-cleido-mastoid. depresses head upon neck and neck upon chest.

Platysma myoides. depresses lower jaw and lower lip.

Trunk.

Pectoralis major. draws arm across front of chest.

Pectoralis minor. depresses point of shoulder, Latissimus dorsi. draws arm downwards and backwards.

Serratus magnus. a.s.sists in raising ribs.

Trapezius. Rhomboideus. backward movements of head and shoulder, Intercostals. raise and depress the ribs.

External oblique. /various forward movements Internal oblique. of trunk Rectus abdominis. compresses abdominal viscera and acts upon pelvis.

Upper Limbs.

Deltoid. carries arm outwards and upwards.

Biceps. flexes elbow and raises arm.

Triceps. extends the forearm.

Brachialis anticus. flexor of elbow.

Supinator longus. flexes the forearm.

Flexor carpi radialis. flexors of wrist.

Flexor carpi ulnaris. " " "