SUGGESTIONS To Teachers
Seeing is believing—more than that, it is often knowing and remembering. The mere reading of a statement is of little value compared with the observation of a fact. Every opportunity should therefore be taken of exhibiting to the pupil the phenomena described, and thus making them real. A microscope is so essential to the understanding of many subjects, that it is indispensable to the proper teaching of Physiology. A suitable instrument and carefully prepared specimens, showing the structure of the bones, the skin, and the blood of various animals, the pigment cells of the eye, etc., may be obtained at a small cost from any good optician.
On naming the subject of a paragraph, the pupil should be prepared to tell all he knows about it. No failure should discourage the teacher in establishing this mode of study and recitation. A little practice will produce the most satisfactory results. The unexpected question and the apt reply develop a certain sharpness and readiness which are worthy of cultivation. The questions for review, or any others that the wit of the teacher may suggest, can be effectively used to break the monotony of a topical recitation, thereby securing the benefits of both systems.
The pupil should expect to be questioned each day upon any subject passed over during the term, and thus the entire knowledge gained will be within his grasp for instant use. While some are reciting to the teacher, let others write on slates or on the blackboard. At the close of the recitation, let all criticise the ideas, the spelling, the use of capitals, the pronunciation, the grammar, and the mode of expression. Greater accuracy and much collateral drill may thus be secured at little expense of valuable school time.
The Introduction is designed merely to furnish suggestive material for the first lesson, preparatory to beginning the study. Other subjects for consideration may be found in the section on Health and Disease, in the Selected Readings, and among the questions given in the Appendix. Where time will allow, the Selected Readings may profitably be used in connection with the topics to which they relate. Questions upon them are so incorporated with those upon the text proper that they may be employed or not, according to the judgment of the teacher.
NOTE.—Interest in the study of Physiology will be much increased by the use of the microscope and prepared slides. These may be obtained from any good optician.
Physiological study in youth is of inestimable value. Precious lives are frequently lost through ignorance. Thousands squander in early years the strength which should have been kept for the work of real life. Habits are often formed in youth which entail weakness and poverty upon manhood, and are a cause of lifelong regret. The use of a strained limb may permanently damage it. Some silly feat of strength may produce an irreparable injury. A thoughtless hour of reading by twilight may impair the sight for life. A terrible accident may happen, and a dear friend perish before our eyes, while we stand by powerless to render the assistance we could so easily give did we "only know what to do." The thousand little hints which may save or lengthen life, may repel or abate disease, and the simple laws which regulate our bodily vigor, should be so familiar that we may be quick to apply them in an emergency. The preservation of health is easier than the cure of disease. Childhood can not afford to wait for the lesson of experience which is learned only when the penalty of violated law has been already incurred, and health irrevocably lost.
NATURE'S LAWS INVIOLABLE.—In infancy, we learn how terribly Nature punishes a violation of certain laws, and how promptly she applies the penalty. We soon find out the peril of fire, falls, edged tools, and the like. We fail, however, to notice the equally sharp and certain punishments which bad habits entail. We are quick to feel the need of food, but not so ready to perceive the danger of an excess. A lack of air drives us at once to secure a supply; foul air is as fatal, but it gives us no warning.
Nature provides a little training for us at the outset of life, but leaves the most for us to learn by bitter experience. So in youth we throw away our strength as if it were a burden of which we desire to be rid. We eat anything, and at any time; do anything we please, and sit up any number of nights with little or no sleep. Because we feel only a momentary discomfort from these physical sins, we fondly imagine when that is gone we are all right again. Our drafts upon our constitution are promptly paid, and we expect this will always be the case; but some day they will come back to us, protested; Nature will refuse to meet our demands, and we shall find ourselves physical bankrupts.
We are furnished in the beginning with a certain vital force upon which we may draw. We can be spendthrifts and waste it in youth, or be wise and so husband it till manhood. Our shortcomings are all charged against this stock. Nature's memory never fails; she keeps her account with perfect exactness. Every physical sin subtracts from the sum and strength of our years. We may cure a disease, but it never leaves us as it found us. We may heal a wound, but the scar still shows. We reap as we sow, and we may either gather in the thorns, one by one, to torment and destroy, or we may rejoice in the happy harvest of a hale old age.
"Not in the World of Light alone,
Where God has built His blazing throne,
Nor yet alone on earth below,
With belted seas that come and go,
And endless isles of sunlit green
Is all thy Maker's glory seen—
Look in upon thy wondrous frame,
Eternal wisdom still the same!"
NOTE.—The following Table of 206 bones is exclusive of the 8 sesamoid bones which occur in pairs at the roots of the thumb and great toe, making 214 as given by Leidy and Draper. Gray omits the bones of the ear, and names 200 as the total number.
THE SKELETON. _ | I. THE HEAD (28 bones.) | | | Frontal Bone (forehead). | | Two Parietal Bones. | | 1. CRANIUM…………..| Two Temporal (temple) Bones. | | (8 bones.) | Sphenoid Bone. | | | Ethmoid (sieve-like bone at root of nose). | | |Occipital Bone (back and base of skull). | | | | | Two Superior Maxillary (upper jaw) Bones. | | | Inferior Maxillary (lower jaw) Bone. | | | Two Malar (cheek) Bones. | | 2. FACE……………..| Two Lachrymal Bones. | | (14 bones.) | Two Turbinated (scroll like) Bones, each | | | side of nose. | | | Two Nasal Bones (Bridge of nose). | | | Vomer (the bone between the nostrils). | | |Two Palate Bones. | | | | | Hammer. | | 3. EARS……………..| Anvil. | |_ (6 bones.) |_Stirrup. | | II. THE TRUNK (54 bones.) | | | Cervical Vertebrć (seven vertebrć of the | | neck). | | 1. SPINAL COLUMN……..| Dorsal Vertebrć (twelve vertebrć of the | | | back). | | | Lumbar Vertebrć (five vertebrć of the | | | loins). | | | | | True Ribs. | | 2. RIBS……………..|False Ribs. | | | | 3. STERNUM (breastbone). | | | | 4. OS HYOIDES (bone at the root of tongue). | | | | | Two Innominata. | |_5. PELVIS……………| Sacrum. | |_Coccyx. | | III. THE LIMBS (124 bones.) | | | Clavicle. | | Shoulder…|__Scapula. | | _ | | 1. UPPER LIMBS……….| | Humerus. | | (64 bones.) | Arm……..|__Ulna and Radius. | | | | | | | Eight Wrist or Carpal | | | | Bones. | | |_Hand…….| Five Metacarpal Bones. | | |__Phalanges (14 bones). | | | | _ | Femur. | | | Leg……..| Patella. | | | |__Tibia and Fibula. | | 2. LOWER LIMBS……….| | |_ (60 bones.) | | Seven Tarsal Bones. |_ | Foot…….| Five Metatarsal Bones. |_ |__Phalanges (14 bones)._
| 1. Uses. | 2. Composition. | 1. FORM, STRUCTURE, | 3. Structure. | ETC., OF THE BONES | 4. Growth. | | 5. Repair. THE SKELETON | |6. The Joints. | | 2. CLASSIFICATION OF | 1. The Head. |_ THE BONES. | 2. The Trunk. |_3. The Limbs. THE SKELETON.
(See page 269.)
THE SKELETON, or framework of the "House we live in," is composed of about 200 bones. [Footnote: The precise number varies in different periods of life. Several which are separated in youth become united in old age. Thus five of the "false vertebrć" at the base of the spine early join in one great bone—the sacrum; while four tiny ones below it often run into a bony mass—the coccyx (Fig. 6); in the child, the sternum is composed of eight pieces, while in the adult it consists of only three. While, however, the number of the bones is uncertain, their relative length is so exact that the length of the entire skeleton, and thence the height of the man, can be obtained by measuring a single one of the principal bones. Fossil bones and those found at Pompeii have the same proportion as our own.]
USES AND FORMS OF THE BONES.—They have three principal uses: 1. To protect the delicate organs; [Footnote: An organ is a portion of the body designed for a particular use, called its function. Thus the heart circulates the blood; the liver produces the bile.] 2. To serve as levers on which the muscles may act to produce motion; and 3. To preserve the shape of the body.
Bones differ in form according to the uses they subserve. For convenience in walking, some are long; for strength and compactness, some are short and thick; for covering a cavity, some are flat; and for special purposes, some are irregular. The general form is such as to combine strength and lightness. For example, all the long bones of the limbs are round and hollow, thus giving with the same weight a greater strength, [Footnote: Cut a sheet of foolscap in two pieces. Roll one half into a compact cylinder, and fold the other into a close, flat strip; support the ends of each and hang weights in the middle until they bend. The superior strength of the roll will astonish one unfamiliar with this mechanical principle. In a rod, the particles break in succession, first those on the outside, and later those in the center. In a tube, the particles are all arranged where they resist the first strain. Iron pillars are therefore cast hollow. Stalks of grass and grain are so light as to bend before a breath of wind, yet are stiff enough to sustain their load of seed. Bone has been found by experiment to possess twice the resisting property of solid oak.] and also a larger surface for the attachment of the muscles.
The Composition of the Bones at maturity is about one part animal to two parts mineral matter. The proportion varies with the age. In youth it is nearly half and half, while in old age the mineral is greatly in excess. By soaking a bone in weak muriatic acid, and thus dissolving the mineral matter, its shape will not change, but its stiffness will disappear, leaving a tough, gristly substance [Footnote: Mix a wineglass of muriatic acid with a pint of water, and place in it a sheep's rib. In a day or two, the bone will become so soft that it can be tied into a knot. In the same way, an egg may be made so pliable that it can be crowded into a narrow- necked bottle, within which it will expand, and become an object of great curiosity to the uninitiated. By boiling bones at a high temperature, the animal matter separates in the form of gelatine. Dogs and cats extract the animal matter from the bones they eat. Fossil bones deposited in the ground during the Geologic period, were found by Cuvier to contain considerable animal matter. Gelatine was actually extracted from the Cambridge mastodon, and made into glue. A tolerably nutritious food might thus be manufactured from bones older than man himself.] (cartilage) which can be bent like rubber.
If the bone be burned in the fire, thus consuming the animal matter, the shape will still be the same, but it will have lost its tenacity, and the beautiful, pure-white residue [Footnote: From bones thus calcined, the phosphorus of the chemist is made. See Steele's "Popular Chemistry," page 114. If the animal matter be not consumed, but only charred, the bone will be black and brittle. In this way, the "boneblack" of commerce is manufactured.] may be crumbled into powder with the fingers.
[Illustration: The Thigh Bone, or Femur, sawed lengthwise.]
We thus see that a bone receives hardness and rigidity from its mineral, and tenacity and elasticity from its animal matter.
The entire bone is at first composed of cartilage, which gradually ossifies or turns to bone. [Footnote: The ossification of the bones on the sides and upper part of the skull, for example, begins by a rounded spot in the middle of each one. From this spot the ossification extends outward in every direction, thus gradually approaching the edges of the bone. When two adjacent bones meet, there will be a line where their edges are in contact with each other, but have not yet united; but when more than two bones meet in this way, there will be an empty space between them at their point of junction. Thus, if you lay down three coins upon the table with their edges touching one another, there will be a three-sided space in the middle between them; if you lay down four coins in the same manner, the space between them will be four-sided. Now at the back part of the head there is a spot where three bones come together in this way, leaving a small, three-sided opening between them: this is called the "posterior fontanelle." On the top of the head, four bones come together, leaving between them a large, four-sided opening: this is called the "anterior fontanelle." These openings are termed the fontanelles, because we can feel the pulsations of the brain through them, like the bubbling of water in a fountain. They gradually diminish in size, owing to the growth of the bony parts around them, and are completely closed at the age of four years after birth.—DALTON.] Certain portions near the joints are long delayed in this process, and by their elasticity assist in breaking the shock of a fall. [Footnote: Frogs and toads, which move by jumping, and consequently receive so many jars, retain these unossified portions (epiphyses) nearly through, life, while alligators and turtles whose position is sprawling, and whose motions are measured do not have them at all—LEIDY] Hence the bones of children are tough, are not readily fractured, and when broken easily heal again; [Footnote: This is only one of the many illustrations of the Infinite care that watches over helpless infancy, until knowledge and ability are acquired to meet the perils of life.] while those of elderly people are liable to fracture, and do not quickly unite.
[Illustration: A thin slice of Bone, highly magnified showing the lacunć, the tiny tubes (canaliculi) radiating from them, and four Haversian canals, three seen crosswise and one lengthwise.]
THE STRUCTURE OF THE BONES—When a bone is sawed lengthwise, it is found to be a compact shell filled with a spongy substance This filling increases in quantity, and becomes more porous at the ends of the bone, thus giving greater size to form a strong joint, while the solid portion increases near the middle, where strength alone is needed. Each fiber of this bulky material diminishes the shock of a sudden blow, and also acts as a beam to brace the exterior wall. The recumbent position of the alligator protects him from falls, and therefore his bones contain very little spongy substance.
In the body, bones are not the dry, dead, blanched things they commonly seem to be, but are moist, living, pinkish structures, covered with a tough membrane, called the per-i-os'-te-um [Footnote: The relations of the periosteum to the bone are very interesting. Instances are on record where the bone has been removed, leaving the periosteum, from which the entire bone was afterward renewed.] (peri, around, and osteon, a bone), while the hollow is filled with marrow, rich in fat, and full of blood vessels. If we examine a thin slice with the microscope, we shall see black spots with lines running in all directions, and looking very like minute insects. These are really little cavities, called la-cu'-nć [Footnote: When the bone is dry, the lacunć are filled with air, which refracts the light, so that none of it reaches the eye, and hence the cavities appear black.] from which radiate tiny tubes. The lacunć are arranged in circles around larger tubes, termed from their discoverer, Haversian canals, which serve as passages for the blood vessels that nourish the bone.
GROWTH OF THE BONES.—By means of this system of canals, the blood circulates as freely through the bones as through any part of the body, The whole structure is constantly but slowly changing, [Footnote: Bone is sometimes produced with surprising rapidity. The great Irish Elk is calculated by Prof. Owen to have cast off and renewed, annually in its antlers eighty pounds of bone.] old material being taken out and new put in. A curious illustration is seen in the fact that if madder be mixed with the food of pigs, it will tinge their bones red.
REPAIR OF THE BONES.—When a bone is broken, the blood at once oozes out of the fractured ends. This soon gives place to a watery fluid, which in a fortnight thickens to a gristly substance, strong enough to hold them in place. Bone matter is then slowly deposited, which in five or six weeks will unite the broken parts. Nature, at first, apparently endeavors to remedy the weakness of the material by excess in the quantity, and so the new portion is larger than the old. But the extra matter will be gradually absorbed, sometimes so perfectly as to leave no trace of the injury. (See p. 271.)
A broken limb should be held in place by splints, or a plaster cast, to enable this process to go on uninterruptedly, and also lest a sudden jar might rupture the partially mended break. For a long time, the new portion consists largely of animal matter, and so is tender and pliable. The utmost care is therefore necessary to prevent a malformation.
THE JOINTS are packed with a soft, smooth cartilage, or gristle, which fits so perfectly as to be airtight. Upon convex surfaces, it is thickest at the middle, and upon concave surfaces, it is thickest at the edge, or where the wear is greatest. In addition, the ends of the bones are covered with a thin membrane, the synovial (sun, with; ovum, an egg), which secretes a viscid fluid, not unlike the white of an egg. This lubricates the joints, and prevents the noise and wear of friction. The body is the only machine that oils itself.
The bones which form the joint are tied with stout ligaments (ligo, I bind), or bands, of a smooth, silvery white tissue, [Footnote: The general term tissue is applied to the various textures of which the organs are composed. For example, the osseous tissue forms the bones; the fibrous tissue, the skin, tendons, and ligaments.] so strong that the bones are sometimes broken without injuring the fastenings.
For convenience, the bones of the skeleton are considered in three divisions: the head, the trunk, and the limbs.
THE BONES OF THE SKULL AND THE FACE form a cavity for the protection of the brain and the four organs of sense, viz.: sight, smell, taste, and hearing. All these bones are immovable except the lower jaw, which is hinged [Footnote: A ring of cartilage is inserted in its joints, something after the manner of a washer in machinery. This follows the movements of the jaw, and admits of freer motion, while it guards against dislocation.] at the back so as to allow for the opening and shutting of the mouth.
THE SKULL is composed, in general, of two compact plates, with a spongy layer between. These are in several pieces, the outer ones being joined by notched edges, sutures (su'tyurs,), in the way carpenters term dovetailing. (See Fig. 4.)
[Illustration: The Skull.—1. frontal bone; 2, parietal bone; 3, temporal bone; 4, the sphenoid bone; 5, ethmoid bone; 6, superior maxillary (upper jaw) bone; 7, malar bone; 8, lachrymal bone; 9, nasal bone; 10, inferior maxillary (lower jaw) bone.]
The peculiar structure and form of the skull afford a perfect shelter for the brain—an organ so delicate that, if unprotected, an ordinary blow would destroy it. Its oval or egg shape adapts it to resist pressure. The smaller and stronger end is in front, where the danger is greatest. Projections before and behind shield the less protected parts. The hard plates are not easy to penetrate. [Footnote: Instances have been known where bullets, striking against the skull, have glanced off, been flattened, or even split into halves. In the Peninsular Campaign, the author saw a man who had been struck in the forehead by a bullet which, instead of penetrating the brain, had followed the skull around to the back of the head, and there passed out.] The spongy packing deadens every blow. [Footnote: An experiment resembling the familiar one of the balls in Natural Philosophy ("Steele's Popular Physics," Fig. 6, p. 26), beautifully illustrates this point. Several balls of ivory are suspended by cords, as in Fig. 5. If A be raised and then let fall, it will transmit the force to B, and that to C, and so on until F is reached, which will fly off with the impulse. If now a ball of spongy bone be substituted for an ivory one anywhere in the line, the force will be checked, and the last ball will not stir.] The separate pieces with their curious joinings disperse any jar which one may receive, and also prevent fractures from spreading.
[Illustration]
The frequent openings in this strong bone box afford safe avenues for the passage of numerous nerves and vessels which communicate between the brain and the rest of the body.
[Illustration: The Spine; the seven vertebrć of the neck, cervical; the twelve of the back, dorsal; the five of the loins, lumbar; a, the sacrum, and b, the coccyx, coming the nine "false vertebrć." (p. 3).]
THE TRUNK has two important cavities. The upper part, or chest, contains the heart and the lungs, and the lower part, or abdomen, holds the stomach, liver, kidneys, and other organs (Fig. 31). The principal bones are those of the spine, the ribs, and the hips.
THE SPINE consists of twenty-four bones, between which are placed pads of cartilage. [Footnote: These pads vary in thickness from one fourth to one half an inch. They become condensed by the weight they bear during the day, so that we are somewhat shorter at evening than in the morning. Their elasticity causes them to resume their usual size during the night, or when we lie down for a time.] A canal is hollowed out of the column for the safe passage of the spinal cord. (See Fig. 50.) Projections (processes) at the back and on either side are abundant for the attachment of the muscles. The packing acts as a cushion to prevent any jar from reaching the brain when we jump or run, while the double curve of the spine also tends to disperse the force of a fall. Thus on every side the utmost caution is taken to guard that precious gem in its casket.
THE PERFECTION OF THE SPINE surpasses all human contrivances. Its various uses seem a bundle of contradictions. A chain of twenty-four bones is made so stiff that it will bear a heavy burden, and so flexible that it will bend like rubber; yet, all the while, it transmits no shock, and even hides a delicate nerve within that would thrill with the slightest touch. Resting upon it, the brain is borne without a tremor; and, clinging to it, the vital organs are carried without fear of harm.
[Illustration: B, the first cervical vertebra, the atlas; A, the atlas, and the second cervical vertebra, the axis; e, the odontoid process; c, the foramen.]
THE SKULL ARTICULATES with (is jointed to) the spine in a peculiar manner. On the top of the upper vertebra (atlas [Footnote: Thus called because, as, in ancient fable, the god Atlas supported the world on his shoulders, so in the body this bone bears the head.]) are two little hollows (a, b, Fig. 7), nicely packed and lined with the synovial membrane, into which fit the corresponding projections on the lower part of the skull, and thus the head can rock to and fro. The second vertebra (axis) has a peg, e, which projects through a hole, c, in the first.
[Illustration: The Thorax or Chest. a, the sternum; b to c, the true ribs; d to h, the false ribs; g, h, the floating ribs; i, k, the dorsal vertebrć.]
The surfaces of both vertebrć are so smooth that they easily glide on each other, and thus, when we move the head side wise, the atlas turns around the peg, e, of the axis.
THE RIBS, also twenty-four in number, are arranged in pairs on each side of the chest. At the back, they are all attached to the spine. In front, the upper seven pairs are tied by cartilages to the breastbone (sternum); three are fastened to each other and to the cartilage above, and two, the floating ribs, are loose.
The natural form of the chest is that of a cone diminishing upward. But, owing to the tightness of the clothing commonly worn, the reverse is often the case. The long, slender ribs give lightness, [Footnote: If the chest wall were in one bone thick enough to resist a blow, it would be unwieldy and heavy As it is, the separate bones bound by cartilages yield gradually, and diffuse the force among them all, and so are rarely broken.] the arched form confers strength, and the cartilages impart elasticity,—properties essential to the protection of the delicate organs within, and to freedom of motion in respiration. (See note, p. 80.)
[Illustration: The Pelvis. a, the sacrum; b, b, the right and the left innominatum.]
THE HIP BONES, called by anatomists the innominata, or nameless bones, form an irregular basin styled the pelvis (pelvis, a basin). In the upper part, is the foot of the spinal column—a wedge-shaped bone termed the sacrum [Footnote: So called because it was anciently offered in sacrifice.] (sacred), firmly planted here between the widespreading and solid bones of the pelvis, like the keystone to an arch, and giving a steady support to the heavy burden above.
TWO SETS OF LIMBS branch from the trunk, viz.: the upper, and the lower. They closely resemble each other. The arm corresponds to the thigh; the forearm, to the leg; the wrist, to the ankle; the fingers, to the toes. The fingers and the toes are so much alike that they receive the same name, digits, while the several bones of both have also the common appellation, phalanges. The differences which exist grow out of their varying uses. The foot is characterized by strength; the hand, by mobility.
[Illustration: The Shoulder Joint. a, the clavicle; b, the scapula.]
1. THE UPPER LIMBS.—THE SHOULDER.—The bones of the shoulder are the collar bone (clavicle), and the shoulder blade (scapula). The clavicle (clavis, a key) is a long, slender bone, shaped like the Italic f. It is fastened at one end to the breastbone and the first rib, and, at the other, to the shoulder blade. (See Fig. 1.) It thus holds the shoulder joint out from the chest, and gives the arm greater play. If it be removed or broken, the head of the arm bone will fall, and the motions of the arm be greatly restricted. [Footnote: Animals which use the forelegs only for support (as the horse, ox, etc.), do not possess this bone. "It is found in those that dig, fly, climb and seize."]
THE SHOULDER BLADE is a thin, flat, triangular bone, fitted to the top and back of the chest, and designed to give a foundation for the muscles of the shoulder.
THE SHOULDER JOINT.—The arm bone, or humerus, articulates with the shoulder blade by a ball-and-socket joint. This consists of a cup-like cavity in the latter bone, and a rounded head in the former, to fit it,— thus affording a free rotary motion. The shallowness of the socket accounts for the frequent dislocation of this joint, but a deeper one would diminish the easy swing of the arm.
[Illustration: Bones of the right Forearm. H, the humerus;
R, the radius; and U, the ulna.]
THE ELBOW.—At the elbow, the humerus articulates with the ulna—a slender bone on the inner side of the forearm—by a hinge joint which admits of motion in only two directions, i. e., backward and forward. The ulna is small at its lower end; the radius, or large bone of the forearm, on the contrary, is small at its upper end, while it is large at its lower end, where it forms the wrist joint. At the elbow, the head of the radius is convex and fits into a shallow cavity in the ulna, while at the wrist the ulna plays in a similar socket in the radius. Thus the radius may roll over and even cross the ulna.
THE WRIST, or carpus, consists of two rows of very irregular bones, one of which articulates with the forearm; the other, with the hand. They are placed side to side, and so firmly fastened as to admit of only a gliding motion. This gives little play, but great strength, elasticity, and power of resisting shocks.
THE HAND.—The metacarpal (meta, beyond; karpos, wrist), or bones of the palm, support each a thumb or a finger. Each finger has three bones, while the thumb has only two. The first bone of the thumb, standing apart from the rest, enjoys a special freedom of motion, and adds greatly to the usefulness of the hand.
[Illustration: Bones of the Hand and the Wrist.]
The first bone (Figs. 11, 12) of each finger is so attached to the corresponding metacarpal bone as to move in several directions upon it, but the other phalanges form hinge joints.
The fingers are named in order: the thumb, the index, the middle, the ring, and the little finger. Their different lengths cause them to fit the hollow of the hand when it is closed, and probably enable us more easily to grasp objects of varying size. If the hand clasps a ball, the tips of the fingers will be in a straight line.
The hand in its perfection belongs only to man. Its elegance of outline, delicacy of mold, and beauty of color have made it the study of artists; while its exquisite mobility and adaptation as a perfect instrument have led many philosophers to attribute man's superiority even more to the hand than to the mind. [Footnote: How constantly the hand aids us in explaining or enforcing a thought! We affirm a fact by placing the hand as if we would rest it firmly on a body; we deny by a gesture putting the false or erroneous proposition away from us; we express doubt by holding the hand suspended, as if hesitating whether to take or reject. When we part from dear friends, or greet them again after long absence, the hand extends toward them as if to retain, or to bring them sooner to us. If a recital or a proposition is revolting, we reject it energetically in gesture as in thought. In a friendly adieu we wave our good wishes to him who is their object; but when it expresses enmity, by a brusque movement we sever every tie. The open hand is carried backward to express fear or horror, as well as to avoid contact; it goes forward to meet the hand of friendship; it is raised suppliantly in prayer toward Him from whom we hope for help; it caresses lovingly the downy cheek of the infant, and rests on its head invoking the blessing of Heaven,—Wonders of the Human Body.]
[Illustration: The Mechanism of the Hip Joint.]
2. THE LOWER LIMBS.—THE HIP—The thigh bone, or femur, is the largest and necessarily the strongest in the skeleton, since at every step it has to bear the weight of the whole body. It articulates with the hip bone by a ball-and-socket joint. Unlike the shoulder joint, the cup here is deep, thus affording less play, but greater strength. It fits so tightly that the pressure of the air largely aids in keeping the bones in place. [Footnote: In order to test this, a hole was bored through a hip bone, so as to admit air into the socket, the thigh bone at once fell out as far as the ligaments would permit. An experiment was also devised whereby a suitably prepared hip joint was placed under the receiver of an air pump. On exhausting the air, the weight of the femur caused it to drop out of the socket, while the readmission of the air raised it to its place. Without this arrangement, the adjacent muscles would have been compelled to bear the additional weight of the thighbone every time it was raised. Now the pressure of the air rids them of this unnecessary burden, and hence they are less easily fatigued—WEBER] Indeed, when the muscles are cut away, great force is required to detach the limbs.
THE KNEE is strengthened by the patella_, or kneepan (patella, little dish), a chestnut-shaped bone firmly fastened over the joint.
The shin bone, or tibia, the large, triangular bone on the inner side of the leg, articulates both with the femur and the foot by hinge joints. The kneejoint is so made, however, as to admit of a slight rotary motion when the limb is not extended.
The fibula (fibula, a clasp), the small, outside bone of the leg, is firmly bound at each end to the tibia. (See Fig. 1.) It is immovable, and, as the tibia bears the principal weight of the body, the chief use of this second bone seems to be to give more surface to which the muscles may be attached. [Footnote: A young man in the hospital at Limoges had lost the middle part of his tibia. The lost bone was not reproduced, but the fibula, the naturally weak and slender part of the leg, became thick and strong enough to support the whole body.—STANLEY'S Lectures.]
THE FOOT.—The general arrangement of the foot is strikingly like that of the hand (Fig. 1). The several parts are the tarsus, the metatarsus, and the phalanges. The graceful arch of the foot, and the numerous bones joined by cartilages, give an elasticity to the step that could never be attained by a single, flat bone. [Footnote: The foot consists of an arch, the base of which is more extended in front than behind, and the whole weight of the body is made to fall on this arch by means of a variety of joints. These joints further enable the foot to be applied, without inconvenience, to rough and uneven surfaces.—HINTON.] The toes naturally lie straight forward in the line of the foot. Few persons in civilized nations, however, have naturally formed feet. The big toe is crowded upon the others, while crossed toes, nails grown-in, enormous joints, corns, and bunions abound.
THE CAUSE OF THESE DEFORMITIES is found in the shape and size of fashionable boots and shoes. The sole ought to be large enough for full play of motion, the uppers should not crowd the toes, and the heels should be low, flat, and broad. As it is, there is a constant warfare between Nature and our shoemakers, [Footnote: When we are measured for boots or shoes, we should stand on a sheet of paper, and have the shoemaker mark with a pencil the exact outline of our feet as they bear our whole weight. When the shoe is made, the sole should exactly cover this outline.] and we are the victims. The narrow point in front pinches our toes, and compels them to override one another; the narrow sole compresses the arch; while the high heel, by throwing all the weight forward on the toes, strains the ankle, and, by sending the pressure where Nature did not design it to fall, causes that joint to become enlarged. The body bends forward to meet the demand of this new motion, and thus loses its uprightness and beauty, making our gait stiff and ungraceful. (See p. 271.)
DISEASES, ETC.—l. Rickets, a disease of early life, is caused by a lack of mineral matter in the bones, rendering them soft and pliable, so that they bend under the weight of the body. They thus become permanently distorted, and of course are weaker than if they were straight, [Footnote: Just here appears an exceedingly beautiful provision. As soon as the disproportion of animal matter ceases, a larger supply of mineral is sent to the weak points, and the bones actually become thicker, denser, harder, and consequently stronger at the very concave part where the stress of pressure is greatest.—WATSON'S Lectures. We shall often have occasion to refer to similar wise and providential arrangements whereby the body is enabled to remedy defects, and to prepare for accidents.] Rickets is most common among children who have inherited a feeble constitution and who are ill fed, or who live in damp, ill-ventilated houses. "Rickety" children should have plenty of fresh air and sunlight, nourishing food, comfortable clothing, and, in short, the best of hygienic care.
2. A Felon is a swelling of the finger or thumb, usually of the last joint. It is marked by an accumulation beneath the periosteum and next the bone. The physician will merely cut through the periosteum, and let out the effete matter.
3. Bowlegs are caused by children standing on their feet before the bones of the lower limbs are strong enough to bear their weight. The custom of encouraging young children to stand by means of a chair or the support of the hand, while the bones are yet soft and pliable, is a cruel one, and liable to produce permanent deformity. Nature will set the child on its feet when the proper time comes.
4. Curvature of the Spine.—When the spine is bent, the packing between the vertebrć becomes compressed on one side into a wedge-like shape. After a time, it will lose its elasticity, and the spine will become distorted. This often occurs in the case of students who bend forward to bring their eyes nearer their books, instead of lifting their books nearer their eyes, or who raise their right shoulder above their left when writing at a desk which is too high. Round shoulders, small, weak lungs, and, frequently, diseases of the spine are the consequences. An erect posture in reading or writing conduces not alone to beauty of form, but also to health of body. We shall learn hereafter that the action of the muscles bears an important part in preserving the symmetry of the spine. Muscular strength comes from bodily activity; hence, one of the best preventives of spinal curvature is daily exercise in the open air.
5. Sprains are produced when the ligaments which bind the bones of a joint are strained, twisted, or torn from their attachments. They are quite as serious as a broken bone, and require careful attention lest they lead to a crippling for life. By premature use a sprained limb may be permanently impaired. Hence, the joint should be kept quiet, even after the immediate pain is gone.
6. A Dislocation is the forcible displacement of a bone from its socket. It is, generally, the result of a fall or a violent blow. The tissues of the joint are often ruptured, while the contraction of the muscles prevents the easy return of the bone to its place. A dislocation should be reduced as soon as possible after the injury, before inflammation supervenes.
1. Why does not a fall hurt a child as much as it does a grown person?
2. Should a young child ever be urged to stand or walk?
3. What is meant by "breaking one's neck"?
4. Should chairs or benches have straight backs?
5. Should a child's feet be allowed to dangle from a high seat?
6. Why can we tell whether a fowl is young by pressing on the point of the breastbone?
7. What is the use of the marrow in the bones?
8. Why is the shoulder so often put out of joint?
9. How can you tie a knot in a bone?
10. Why are high pillows injurious?
11. Is a stooping posture a healthful position?
12. Should a boot have a heel piece?
13. Why should one always sit and walk erect?
14. Why does a young child creep rather than walk?
15. What is the natural direction of the big toe?
16. What is the difference between a sprain and a fracture? A dislocation?
17. Does the general health of the system affect the strength of the bones?
18. Is living bone sensitive? Ans.—Scrape a bone, and its vessels bleed; cut or bore a bone, and its granulations sprout up; break a bone, and it will heal; cut a piece away, and more bone will readily be produced; hurt it in any way, and it inflames; burn it, and it dies. Take any proof of sensibility but the mere feeling of pain, and it will answer to the proof.—BELL'S Anatomy. Animal sensibility would be inconvenient; it is therefore not to be found except in diseased bone, where it sometimes exhibits itself too acutely.—TODD'S Cyclopedia of Anatomy.
19. Is the constitution of bone the same in animals as in man? Ans.—The bones of quadrupeds do not differ much from those of man. In general they are of a coarser texture, and in some, as in those of the elephant's head, we find extensive air cells.—TODD'S Anatomy.
"Behold the outward moving frame,
Its living marbles jointed strong
With glistening band and silvery thong,
And link'd to reason's guiding reins
By myriad rings in trembling chains,
Each graven with the threaded zone
Which claims it as the Master's own."
| 1. The Use of the Muscles. | 2. Contractility of the Muscles. | 3. Arrangement of the Muscles. | 1. THE USE, STRUCTURE | 4. The two Kinds of Muscles. | AND ACTION OF THE | 5. The Structure of the Muscles. | MUSCLES. | 6. The Tendons for Fastening Muscles. | | 7. The Muscles and Bones as Levers. | | 8. The Effect of Big Joints. | | 9. Action of the Muscles in Walking. | |10. Action of the Muscles in Walking. | | 2. THE MUSCULAR SENSE. | | 3. HYGIENE OF THE | 1. Necessity of Exercise. | MUSCLES. | 2. Time for Exercise. | | 3. Kinds of Exercise. | | 4. WONDERS OF THE MUSCLES. | | | 1. St. Vitus's Dance. | | 2. Convulstions. | | 3. Locked-jaw. |5. DISEASES. | 4. Gout. | 5. Rheumatism. | 6. Lumbago. | 7. A Ganglion.
[Illustration]
THE USE OF THE MUSCLES.—The skeleton is the image of death. Its unsightly appearance instinctively repels us. We have seen, however, what uses it subserves in the body, and how the ugly-looking bones abound in nice contrivances and ingenious workmanship. In life, the framework is hidden by the flesh. This covering is a mass of muscles, which by their arrangement and their properties not only give form and symmetry to the body, but also produce its varied movements.
In Fig. 14, we see the large exterior muscles. Beneath these are many others; while deeply hidden within are tiny, delicate ones, too small to be seen with the naked eye. There are, in all, about five hundred, each having its special use, and all working in exquisite harmony and perfection.
CONTRACTILITY.—The peculiar property of the muscles is their power of contraction, whereby they decrease in length and increase in thickness. [Footnote: The maximum force of this contraction has been estimated as high as from eighty-five to one hundred and fourteen pounds per square inch.] This may be caused by an effort of the will, by cold, by a sharp blow, etc. It does not cease at death, but, in certain cold-blooded animals, a contraction of the muscles is often noticed long after the head has been cut off.
ARRANGEMENT OF THE MUSCLES. [Footnote: "Could we behold properly the muscular fibers in operation, nothing, as a mere mechanical exhibition, can be conceived more superb than the intricate and combined actions that must take place during our most common movements. Look at a person running or leaping, or watch the motions of the eye. How rapid, how delicate, how complicated, and yet how accurate, are the motions required! Think of the endurance of such a muscle as the heart, that can contract, with a force equal to sixty pounds, seventy-five times every minute, for eighty years together, without being weary."]—The muscles are nearly all arranged in pairs, each with its antagonist, so that, as they contract and expand alternately, the bone to which they are attached is moved to and fro. (See p. 275.)
If you grasp the arm tightly with your hand just above the elbow joint, and bend the forearm, you will feel the muscle on the inside (biceps, a, Fig. 14) swell, and become hard and prominent, while the outside muscle (triceps, f) will be relaxed. Now straighten the arm, and the swelling and hardness of the inside muscle will vanish, while the outside one will, in turn, become rigid. So, also, if you clasp the arm just below the elbow, and then open and shut the fingers, you can feel the alternate expanding and relaxing of the muscles on opposite sides of the arms.
If the muscles on one side of the face become palsied, those on the other side will draw the mouth that way. Squinting is caused by one of the straight muscles of the eye (Fig. 17) contracting more strongly than its antagonist.
KINDS OF MUSCLES.—There are two kinds of muscles, the voluntary, which are under the control of our will, and the involuntary, which are not. Thus our limbs stiffen or relax as we please, but the heart beats on by day and by night. The eyelid, however, is both voluntary and involuntary, so that while we wink constantly without effort, we can, to a certain extent, restrain or control the motion.
STRUCTURE OF THE MUSCLES.—If we take a piece of lean beef and wash out the red color, we can easily detect the fine fibers of which the meat is composed. In boiling corned beef for the table, the fibers often separate, owing to the dissolving of the delicate tissue which bound them together. By means of the microscope, we find that these fibers are made up of minute filaments (fibrils), and that each fibril is composed of a row of small cells arranged like a string of beads. This gives the muscles a peculiar striped (striated) appearance. [Footnote: The involuntary muscles consist generally of smooth, fibrous tissue, and form sheets or membranes in the walls of hollow organs. By their contraction they change the size of cavities which they inclose. Some functions, however, like the action of the heart, or the movements of deglutition (swallowing), require the rapid, vigorous contraction, characteristic of the voluntary muscular tissue—FLINT.] (See p. 276.) The cells are filled with a fluid or semifluid mass of living (protoplasmic) matter.
[Illustration: Microscopic view of a Muscle, showing, at one end, the fibrillć; and, at the other, the disks, or cells, of the fiber.]
The binding of so many threads into one bundle [Footnote: We shall learn hereafter how these fibers are firmly tied together by a mesh of fine connective tissue which dissolves in boiling, as just described] confers great strength, according to a mechanical principle that we see exemplified in suspension bridges, where the weight is sustained, not by bars of iron, but by small wires twisted into massive ropes.
[Illustration: Tendons of the Hand.]