Practical Experiments; Use of the Microscope; Additional
Experiments;
Surface Anatomy and Landmarks.
Glossary
Index
Chapter I.
Introduction.
1. The Study of Physiology. We are now to take up a new study, and in a
field quite different from any we have thus far entered. Of all our
other studies,—mathematics, physics, history, language,—not one comes
home to us with such peculiar interest as does physiology, because this
is the study of ourselves.
Every thoughtful young person must have asked himself a hundred
questions about the problems of human life: how it can be that the few
articles of our daily food—milk, bread, meats, and similar things—build
up our complex bodies, and by what strange magic they are transformed
into hair, skin, teeth, bones, muscles, and blood.
How is it that we can lift these curtains of our eyes and behold all
the wonders of the world around us, then drop the lids, and though at
noonday, are instantly in total darkness? How does the minute structure
of the ear report to us with equal accuracy the thunder of the tempest,
and the hum of the passing bee? Why is breathing so essential to our
life, and why cannot we stop breathing when we try? Where within us,
and how, burns the mysterious fire whose subtle heat warms us from the
first breath of infancy till the last hour of life?
These and scores of similar questions it is the province of this deeply
interesting study of physiology to answer.
2. What Physiology should Teach us. The study of physiology is not only
interesting, but it is also extremely useful. Every reasonable person
should not only wish to acquire the knowledge how best to protect and
preserve his body, but should feel a certain profound respect for an
organism so wonderful and so perfect as his physical frame. For our
bodies are indeed not ourselves, but the frames that contain us,—the
ships in which we, the real selves, are borne over the sea of life. He
must be indeed a poor navigator who is not zealous to adorn and
strengthen his ship, that it may escape the rocks of disease and
premature decay, and that the voyage of his life may be long, pleasant,
and successful.
But above these thoughts there rises another,—that in studying
physiology we are tracing the myriad lines of marvelous ingenuity and
forethought, as they appear at every glimpse of the work of the Divine
Builder. However closely we study our bodily structure, we are, at our
best, but imperfect observers of the handiwork of Him who made us as we
are.
3. Distinctive Characters of Living Bodies. Even a very meagre
knowledge of the structure and action of our bodies is enough to reveal
the following distinctive characters: our bodies are continually
breathing, that is, they take in oxygen from the surrounding air; they
take in certain substances known as food, similar to those composing
the body, which are capable through a process called oxidation, or
through other chemical changes, of setting free a certain amount of
energy.
Again, our bodies are continually making heat and giving it out to
surrounding objects, the production and the loss of heat being so
adjusted that the whole body is warm, that is, of a temperature higher
than that of surrounding objects. Our bodies, also, move themselves,
either one part on another, or the whole body from place to place. The
motive power is not from the outside world, but the energy of their
movements exists in the bodies themselves, influenced by changes in
their surroundings. Finally, our bodies are continually getting rid of
so-called waste matters, which may be considered products of the
oxidation of the material used as food, or of the substances which make
up the organism.
4. The Main Problems of Physiology briefly Stated. We shall learn in a
subsequent chapter that the living body is continually losing energy,
but by means of food is continually restoring its substance and
replenishing its stock of energy. A great deal of energy thus stored up
is utilized as mechanical work, the result of physical movements. We
shall learn later on that much of the energy which at last leaves the
body as heat, exists for a time within the organism in other forms than
heat, though eventually transformed into heat. Even a slight change in
the surroundings of the living body may rapidly, profoundly, and in
special ways affect not only the amount, but the kind of energy set
free. Thus the mere touch of a hair may lead to such a discharge of
energy, that a body previously at rest may be suddenly thrown into
violent convulsions. This is especially true in the case of tetanus, or
lockjaw.
The main problem we have to solve in the succeeding pages is to
ascertain how it is that our bodies can renew their substance and
replenish the energy which they are continually losing, and can,
according to the nature of their surroundings, vary not only the
amount, but the kind of energy which they set free.
5. Technical Terms Defined. All living organisms are studied usually
from two points of view: first, as to their form and structure; second,
as to the processes which go on within them. The science which treats
of all living organisms is called biology. It has naturally two
divisions,—morphology, which treats of the form and structure of living
beings, and physiology, which investigates their functions, or the
special work done in their vital processes.
The word anatomy, however, is usually employed instead of morphology.
It is derived from two Greek words, and means the science of
dissection. Human anatomy then deals with the form and structure of the
human body, and describes how the different parts and organs are
arranged, as revealed by observation, by dissection, and by the
microscope.
Histology is that part of anatomy which treats of the minute structure
of any part of the body, as shown by the microscope.
Human physiology describes the various processes that go on in the
human body in health. It treats of the work done by the various parts
of the body, and of the results of the harmonious action of the several
organs. Broadly speaking, physiology is the science which treats of
functions. By the word function is meant the special work which an
organ has to do. An organ is a part of the body which does a special
work. Thus the eye is the organ of sight, the stomach of digestion, and
the lungs of breathing.
It is plain that we cannot understand the physiology of our bodies
without a knowledge of their anatomy. An engineer could not understand
the working of his engine unless well acquainted with all its parts,
and the manner in which they were fitted together. So, if we are to
understand the principles of elementary physiology, we must master the
main anatomical facts concerning the organs of the body before
considering their special functions.
As a branch of study in our schools, physiology aims to make clear
certain laws which are necessary to health, so that by a proper
knowledge of them, and their practical application, we may hope to
spend happier and more useful, because healthier, lives. In brief, the
study of hygiene, or the science of health, in the school curriculum,
is usually associated with that of physiology.[1]
6. Chemical Elements in the Body. All of the various complex substances
found in nature can be reduced by chemical analysis to about 70
elements, which cannot be further divided. By various combinations of
these 70 elements all the substances known to exist in the world of
nature are built up. When the inanimate body, like any other substance,
is submitted to chemical analysis, it is found that the bone, muscle,
teeth, blood, etc., may be reduced to a few chemical elements.
In fact, the human body is built up with 13 of the 70 elements, namely:
oxygen, hydrogen, nitrogen, chlorine, fluorine, carbon, phosphorus,
sulphur, calcium, potassium, sodium, magnesium, and iron. Besides
these, a few of the other elements, as silicon, have been found; but
they exist in extremely minute quantities.
The following table gives the proportion in which these various
elements are present:
Oxygen 62.430 per cent
Carbon 21.150 ” ”
Hydrogen 9.865 ” ”
Nitrogen 3.100 ” ”
Calcium 1.900 ” ”
Phosphorus 0.946 ” ”
Potassium 0.230 ” ”
Sulphur 0.162 ” ”
Chlorine 0.081 ” ”
Sodium 0.081 ” ”
Magnesium 0.027 ” ”
Iron 0.014 ” ”
Fluorine 0.014 ” ”
———
100.000
As will be seen from this table, oxygen, hydrogen, and nitrogen, which
are gases in their uncombined form, make up ¾ of the weight of the
whole human body. Carbon, which exists in an impure state in charcoal,
forms more than ⅕ of the weight of the body. Thus carbon and the three
gases named, make up about 96 per cent of the total weight of the body.
7. Chemical Compounds in the Body. We must keep in mind that, with
slight exceptions, none of these 13 elements exist in their elementary
form in the animal economy. They are combined in various proportions,
the results differing widely from the elements of which they consist.
Oxygen and hydrogen unite to form water, and water forms more than ⅔ of
the weight of the whole body. In all the fluids of the body, water acts
as a solvent, and by this means alone the circulation of nutrient
material is possible. All the various processes of secretion and
nutrition depend on the presence of water for their activities.
8. Inorganic Salts. A large number of the elements of the body unite
one with another by chemical affinity and form inorganic salts. Thus
sodium and chlorine unite and form chloride of sodium, or common salt.
This is found in all the tissues and fluids, and is one of the most
important inorganic salts the body contains. It is absolutely necessary
for continued existence. By a combination of phosphorus with sodium,
potassium, calcium, and magnesium, the various phosphates are formed.
The phosphates of lime and soda are the most abundant of the salts of
the body. They form more than half the material of the bones, are found
in the teeth and in other solids and in the fluids of the body. The
special place of iron is in the coloring matter of the blood. Its
various salts are traced in the ash of bones, in muscles, and in many
other tissues and fluids. These compounds, forming salts or mineral
matters that exist in the body, are estimated to amount to about 6 per
cent of the entire weight.
9. Organic Compounds. Besides the inorganic materials, there exists in
the human body a series of compound substances formed of the union of
the elements just described, but which require the agency of living
structures. They are built up from the elements by plants, and are
called organic. Human beings and the lower animals take the organized
materials they require, and build them up in their own bodies into
still more highly organized forms.
The organic compounds found in the body are usually divided into three
great classes:
Proteids, or albuminous substances.
Carbohydrates (starches, sugars, and gums).
Fats.
The extent to which these three great classes of organic materials of
the body exist in the animal and vegetable kingdoms, and are utilized
for the food of man, will be discussed in the chapter on food (Chapter
V.). The Proteids, because they contain the element nitrogen and the
others do not, are frequently called nitrogenous, and the other two are
known as non-nitrogenous substances. The proteids, the type of which is
egg albumen, or the white of egg, are found in muscle and nerve, in
glands, in blood, and in nearly all the fluids of the body. A human
body is estimated to yield on an average about 18 per cent of
albuminous substances. In the succeeding chapters we shall have
occasion to refer to various and allied forms of proteids as they exist
in muscle (myosin), coagulated blood (fibrin), and bones (gelatin).
The Carbohydrates are formed of carbon, hydrogen, and oxygen, the last
two in the proportion to form water. Thus we have animal starch, or
glycogen, stored up in the liver. Sugar, as grape sugar, is also found
in the liver. The body of an average man contains about 10 per cent of
Fats. These are formed of carbon, hydrogen, and oxygen, in which the
latter two are not in the proportion to form water. The fat of the body
consists of a mixture which is liquid at the ordinary temperature.
Now it must not for one moment be supposed that the various chemical
elements, as the proteids, the salts, the fats, etc., exist in the body
in a condition to be easily separated one from another. Thus a piece of
muscle contains all the various organic compounds just mentioned, but
they are combined, and in different cases the amount will vary. Again,
fat may exist in the muscles even though it is not visible to the naked
eye, and a microscope is required to show the minute fat cells.
10. Protoplasm. The ultimate elements of which the body is composed
consist of “masses of living matter,” microscopic in size, of a
material commonly called protoplasm.[2] In its simplest form protoplasm
appears to be a homogeneous, structureless material, somewhat
resembling the raw white of an egg. It is a mixture of several chemical
substances and differs in appearance and composition in different parts
of the body.
Protoplasm has the power of appropriating nutrient material, of
dividing and subdividing, so as to form new masses like itself. When
not built into a tissue, it has the power of changing its shape and of
moving from place to place, by means of the delicate processes which it
puts forth. Now, while there are found in the lowest realm of animal
life, organisms like the amœba of stagnant pools, consisting of nothing
more than minute masses of protoplasm, there are others like them which
possess a small central body called a nucleus. This is known as
nucleated protoplasm.
Illustration: Fig. 1.—Diagram of a Cell.
A, nucleus;
B, nucleolus;
C, protoplasm. (Highly magnified)
11. Cells. When we carry back the analysis of an organized body as far
as we can, we find every part of it made up of masses of nucleated
protoplasm of various sizes and shapes. In all essential features these
masses conform to the type of protoplasmic matter just described. Such
bodies are called cells. In many cells the nucleus is finely granular
or reticulated in appearance, and on the threads of the meshwork may be
one or more enlargements, called nucleoli. In some cases the protoplasm
at the circumference is so modified as to give the appearance of a
limiting membrane called the cell wall. In brief, then, a cell is a
mass of nucleated protoplasm; the nucleus may have a nucleolus, and the
cell may be limited by a cell wall. Every tissue of the human body is
formed through the agency of protoplasmic cells, although in most cases
the changes they undergo are so great that little evidence remains of
their existence.
There are some organisms lower down in the scale, whose whole activity
is confined within the narrow limits of a single cell. Thus, the amœba
begins its life as a cell split off from its parent. This divides in
its turn, and each half is a complete amœba. When we come a little
higher than the amœba, we find organisms which consist of several
cells, and a specialization of function begins to appear. As we ascend
in the animal scale, specialization of structure and of function is
found continually advancing, and the various kinds of cells are grouped
together into colonies or organs.
12. Cells and the Human Organism. If the body be studied in its
development, it is found to originate from a single mass of nucleated
protoplasm, a single cell with a nucleus and nucleolus. From this
original cell, by growth and development, the body, with all its
various tissues, is built up. Many fully formed organs, like the liver,
consist chiefly of cells. Again, the cells are modified to form fibers,
such as tendon, muscle, and nerve. Later on, we shall see the white
blood corpuscles exhibit all the characters of the amœba (Fig. 2). Even
such dense structures as bone, cartilage, and the teeth are formed from
cells.
Illustration: Fig. 2.—Amœboid Movement of a Human White Blood
Corpuscle. (Showing various phases of movement.)
In short, cells may be regarded as the histological units of animal
structures; by the combination, association, and modification of these
the body is built up. Of the real nature of the changes going on within
the living protoplasm, the process of building up lifeless material
into living structures, and the process of breaking down by which waste
is produced, we know absolutely nothing. Could we learn that, perhaps
we should know the secret of life.
13. Kinds of Cells. Cells vary greatly in size, some of the smallest
being only 1/3500 an inch or less in diameter. They also vary greatly
in form, as may be seen in Figs. 3 and 5. The typical cell is usually
_globular_ in form, other shapes being the result of pressure or of
similar modifying influences. The globular, as well as the large, flat
cells, are well shown in a drop of saliva. Then there are the
_columnar_ cells, found in various parts of the intestines, in which
they are closely arranged side by side. These cells sometimes have on
the free surface delicate prolongations called cilia. Under the
microscope they resemble a wave, as when the wind blows over a field of
grain (Fig. 5). There are besides cells known as _spindle, stellate,
squamous_ or pavement, and various other names suggested by their
shapes. Cells are also described as to their contents. Thus _fat_ and
_pigment_ cells are alluded to in succeeding sections. Again, they may
be described as to their functions or location or the tissue in which
they are found, as _epithelial_ cells, _blood_ cells (corpuscles, Figs.
2 and 66), _nerve_ cells (Fig. 4), and _connective-tissue_ cells.
14. Vital Properties of Cells. Each cell has a life of its own. It
manifests its vital properties in that it is born, grows, multiplies,
decays, and at last dies.[3] During its life it assimilates food,
works, rests, and is capable of spontaneous motion and frequently of
locomotion. The cell can secrete and excrete substance, and, in brief,
presents nearly all the phenomena of a human being.
Cells are produced only from cells by a process of self-division,
consisting of a cleavage of the whole cell into parts, each of which
becomes a separate and independent organism. Cells rapidly increase in
size up to a certain definite point which they maintain during adult
life. A most interesting quality of cell life is motion, a beautiful
form of which is found in ciliated epithelium. Cells may move actively
and passively. In the blood the cells are swept along by the current,
but the white corpuscles, seem able to make their way actively through
the tissues, as if guided by some sort of instinct.
Illustration: Fig. 3.—Various Forms of Cells.
A, columnar cells found lining various parts of the intestines (called
_columnar epithelium_);
B, cells of a fusiform or spindle shape found in the loose tissue
under the skin and in other parts (called _connective-tissue cells_);
C, cell having many processes or projections—such are found in
connective tissue, D, primitive cells composed of protoplasm with
nucleus, and having no cell wall. All are represented about 400 times
their real size.
Some cells live a brief life of 12 to 24 hours, as is probably the case
with many of the cells lining the alimentary canal; others may live for
years, as do the cells of cartilage and bone. In fact each cell goes
through the same cycle of changes as the whole organism, though
doubtless in a much shorter time. The work of cells is of the most
varied kind, and embraces the formation of every tissue and
product,—solid, liquid, or gaseous. Thus we shall learn that the cells
of the liver form bile, those of the salivary glands and of the glands
of the stomach and pancreas form juices which aid in the digestion of
food.
15. The Process of Life. All living structures are subject to constant
decay. Life is a condition of incessant changes, dependent upon two
opposite processes, repair and decay. Thus our bodies are not composed
of exactly the same particles from day to day, or even from one moment
to another, although to all appearance we remain the same individuals.
The change is so gradual, and the renewal of that which is lost may be
so exact, that no difference can be noticed except at long intervals of
time.[4] (See under “Bacteria,” Chapter XIV.)
The entire series of chemical changes that take place in the living
body, beginning with assimilation and ending with excretion, is
included in one word, metabolism. The process of building up living
material, or the change by which complex substances (including the
living matter itself) are built up from simpler materials, is called
anabolism. The breaking down of material into simple products, or the
changes in which complex materials (including the living substance) are
broken down into comparatively simple products, is known as katabolism.
This reduction of complex substances to simple, results in the
production of animal force and energy. Thus a complex substance, like a
piece of beef-steak, is built up of a large number of molecules which
required the expenditure of force or energy to store up. Now when this
material is reduced by the process of digestion to simpler bodies with
fewer molecules, such as carbon dioxid, urea, and water, the force
stored up in the meat as potential energy becomes manifest and is used
as active life-force known as _kinetic energy_.
16. Epithelium. Cells are associated and combined in many ways to form
a simple tissue. Such a simple tissue is called an epithelium or
surface-limiting tissue, and the cells are known as epithelial cells.
These are united by a very small amount of a cement substance which
belongs to the proteid class of material. The epithelial cells, from
their shape, are known as squamous, columnar, glandular, or ciliated.
Again, the cells may be arranged in only a single layer, or they may be
several layers deep. In the former case the epithelium is said to be
simple; in the latter, stratified. No blood-vessels pass into these
tissues; the cells derive their nourishment by the imbibition of the
plasma of the blood exuded into the subjacent tissue.
Illustration: Fig. 4.—Nerve Cells from the Gray Matter of the
Cerebellum. (Magnified 260 diameters.)
17. Varieties of Epithelium. The squamous or pavement epithelium
consists of very thin, flattened scales, usually with a small nucleus
in the center. When the nucleus has disappeared, they become mere horny
plates, easily detached. Such cells will be described as forming the
outer layer of the skin, the lining of the mouth and the lower part of
the nostrils.
The columnar epithelium consists of pear-shaped or elongated cells,
frequently as a single layer of cells on the surface of a mucous
membrane, as on the lining of the stomach and intestines, and the free
surface of the windpipe and large air-tubes.
The glandular or spheroidal epithelium is composed of round cells or
such as become angular by mutual pressure. This kind forms the lining
of glands such as the liver, pancreas, and the glands of the skin.
The ciliated epithelium is marked by the presence of very fine
hair-like processes called cilia, which develop from the free end of
the cell and exhibit a rapid whip-like movement as long as the cell is
alive. This motion is always in the same direction, and serves to carry
away mucus and even foreign particles in contact with the membrane on
which the cells are placed. This epithelium is especially common in the
air passages, where it serves to keep a free passage for the entrance
and exit of air. In other canals a similar office is filled by this
kind of epithelium.
18. Functions of Epithelial Tissues. The epithelial structures may be
divided, as to their functions, into two main divisions. One is chiefly
protective in character. Thus the layers of epithelium which form the
superficial layer of the skin have little beyond such an office to
discharge. The same is to a certain extent true of the epithelial cells
covering the mucous membrane of the mouth, and those lining the air
passages and air cells of the lungs.
Illustration: Fig. 5.—Various Kinds of Epithelial Cells
A, columnar cells of intestine;
B, polyhedral cells of the conjunctiva;
C, ciliated conical cells of the trachea;
D, ciliated cell of frog’s mouth;
E, inverted conical cell of trachea;
F, squamous cell of the cavity of mouth, seen from its broad surface;
G, squamous cell, seen edgeways.
The second great division of the epithelial tissues consists of those
whose cells are formed of highly active protoplasm, and are busily
engaged in some sort of secretion. Such are the cells of glands,—the
cells of the salivary glands, which secrete the saliva, of the gastric
glands, which secrete the gastric juice, of the intestinal glands, and
the cells of the liver and sweat glands.
19. Connective Tissue. This is the material, made up of fibers and
cells, which serves to unite and bind together the different organs and
tissues. It forms a sort of flexible framework of the body, and so
pervades every portion that if all the other tissues were removed, we
should still have a complete representation of the bodily shape in
every part. In general, the connective tissues proper act as packing,
binding, and supporting structures. This name includes certain tissues
which to all outward appearance vary greatly, but which are properly
grouped together for the following reasons: first, they all act as
supporting structures; second, under certain conditions one may be
substituted for another; third, in some places they merge into each
other.
All these tissues consist of a ground-substance, or matrix, cells, and
fibers. The ground-substance is in small amount in connective tissues
proper, and is obscured by a mass of fibers. It is best seen in hyaline
cartilage, where it has a glossy appearance. In bone it is infiltrated
with salts which give bone its hardness, and make it seem so unlike
other tissues. The cells are called connective-tissue corpuscles,
cartilage cells, and bone corpuscles, according to the tissues in which
they occur. The fibers are the white fibrous and the yellow elastic
tissues.
The following varieties are usually described:
Connective Tissues Proper:
White Fibrous Tissue.
Yellow Elastic Tissue.
Areolar or Cellular Tissue.
Adipose or Fatty Tissue.
Adenoid or Retiform Tissue.
Cartilage (Gristle):
Hyaline.
White Fibro-cartilage.
Yellow Fibro-cartilage.
Bone and Dentine of Teeth.
20. White Fibrous Tissue. This tissue consists of bundles of very
delicate fibrils bound together by a small amount of cement substance.
Between the fibrils protoplasmic masses (connective-tissue corpuscles)
are found. These fibers may be found so interwoven as to form a sheet,
as in the periosteum of the bone, the fasciæ around muscles, and the
capsules of organs; or they may be aggregated into bundles and form
rope-like bands, as in the ligaments of joints and the tendons of
muscles. On boiling, this tissue yields gelatine. In general, where
white fibrous tissue abounds, structures are held together, and there
is flexibility, but little or no distensibility.
Illustration: Fig. 6.—White Fibrous Tissue. (Highly magnified.)
21. Yellow Elastic Tissue. The fibers of yellow elastic tissue are much
stronger and coarser than those of the white. They are yellowish, tend
to curl up at the ends, and are highly elastic. It is these fibers
which give elasticity to the skin and to the coats of the arteries. The
typical form of this tissue occurs in the ligaments which bind the
vertebræ together (Fig. 26), in the true vocal cords, and in certain
ligaments of the larynx. In the skin and fasciæ, the yellow elastic is
found mixed with white fibrous and areolar tissues. It does not yield
gelatine on boiling, and the cells are, if any, few.
Illustration: Fig. 7.—Yellow Elastic Tissue. (Highly magnified.)
22. Areolar or Cellular Tissue. This consists of bundles of delicate
fibers interlacing and crossing one another, forming irregular spaces
or meshes. These little spaces, in health, are filled with fluid that
has oozed out of the blood-vessels. The areolar tissue forms a
protective covering for the tissues of delicate and important organs.
23. Adipose or Fatty Tissue. In almost every part of the body the
ordinary areolar tissue contains a variable quantity of adipose or
fatty tissue. Examined by the microscope, the fat cells consist of a
number of minute sacs of exceedingly delicate, structureless membrane
filled with oil. This is liquid in life, but becomes solidified after
death. This tissue is plentiful beneath the skin, in the abdominal
cavity, on the surface of the heart, around the kidneys, in the marrow
of bones, and elsewhere. Fat serves as a soft packing material. Being a
poor conductor, it retains the heat, and furnishes a store rich in
carbon and hydrogen for use in the body.
24. Adenoid or Retiform Tissue. This is a variety of connective tissue
found in the tonsils, spleen, lymphatic glands, and allied structures.
It consists of a very fine network of cells of various sizes. The
tissue combining them is known as adenoid or gland-like tissue.
Illustration: Fig. 8.—Fibro-Cartilage Fibers. (Showing network
surrounded cartilage cells.)
25. Cartilage. Cartilage, or gristle, is a tough but highly elastic
substance. Under the microscope cartilage is seen to consist of a
matrix, or base, in which nucleated cells abound, either singly or in
groups. It has sometimes a fine ground-glass appearance, when the
cartilage is spoken of as hyaline. In other cases the matrix is almost
replaced by white fibrous tissue. This is called white fibro-cartilage,
and is found where great strength and a certain amount of rigidity are
required.
Again, there is between the cells a meshwork of yellow elastic fibers,
and this is called yellow fibro-cartilage (Fig. 8). The hyaline
cartilage forms the early state of most of the bones, and is also a
permanent coating for the articular ends of long bones. The white
fibro-cartilage is found in the disks between the bodies of the
vertebræ, in the interior of the knee joint, in the wrist and other
joints, filling the cavities of the bones, in socket joints, and in the
grooves for tendons. The yellow fibro-cartilage forms the expanded part
of the ear, the epiglottis, and other parts of the larynx.
26. General Plan of the Body. To get a clearer idea of the general plan
on which the body is constructed, let us imagine its division into
perfectly equal parts, one the right and the other the left, by a great
knife severing it through the median, or middle line in front, backward
through the spinal column, as a butcher divides an ox or a sheep into
halves for the market. In a section of the body thus planned the skull
and the spine together are shown to have formed a tube, containing the
brain and spinal cord. The other parts of the body form a second tube
(ventral) in front of the spinal or dorsal tube. The upper part of the
second tube begins with the mouth and is formed by the ribs and
breastbone. Below the chest in the abdomen, the walls of this tube
would be made up of the soft parts.
Illustration: Fig. 9.—Diagrammatic Longitudinal Section of the Trunk
and Head. (Showing the dorsal and the ventral tubes.)
A, the cranial cavity;
B, the cavity of the nose;
C, the mouth;
D, the alimentary canal represented as a simple straight tube;
E, the sympathetic nervous system;
F, heart;
G, diaphragm;
H, stomach;
K, end of spinal portion of cerebro-spinal nervous system.
We may say, then, that the body consists of two tubes or cavities,
separated by a bony wall, the dorsal or nervous tube, so called because
it contains the central parts of the nervous system; and the visceral
or ventral tube, as it contains the viscera, or general organs of the
body, as the alimentary canal, the heart, the lungs, the sympathetic
nervous system, and other organs.
The more detailed study of the body may now be begun by a description
of the skeleton or framework which supports the soft parts.
Experiments.
For general directions and explanations and also detailed suggestions
for performing experiments, see Chapter XV.
Experiment 1. _To examine squamous epithelium._ With an ivory
paper-knife scrape the back of the tongue or the inside of the lips or
cheek; place the substance thus obtained upon a glass slide; cover it
with a thin cover-glass, and if necessary add a drop of water. Examine
with the microscope, and the irregularly formed epithelial cells will
be seen.
Experiment 2. _To examine ciliated epithelium._ Open a frog’s mouth,
and with the back of a knife blade gently scrape a little of the
membrane from the roof of the mouth. Transfer to a glass slide, add a
drop of salt solution, and place over it a cover-glass with a hair
underneath to prevent pressure upon the cells. Examine with a
microscope under a high power. The cilia move very rapidly when quite
fresh, and are therefore not easily seen.
For additional experiments which pertain to the microscopic examination
of the elementary tissues and to other points in practical histology,
see Chapter XV.
Note. Inasmuch as most of the experimental work of this chapter depends
upon the use of the microscope and also necessarily assumes a knowledge
of facts which are discussed later, it would be well to postpone
experiments in histology until they can be more satisfactorily handled
in connection with kindred topics as they are met with in the
succeeding chapters.]
Chapter II.
The Bones.
27. The Skeleton. Most animals have some kind of framework to support
and protect the soft and fleshy parts of their bodies. This framework
consists chiefly of a large number of bones, and is called the
skeleton. It is like the keel and ribs of a vessel or the frame of a
house, the foundation upon which the bodies are securely built.
There are in the adult human body 200 distinct bones, of many sizes and
shapes. This number does not, however, include several small bones
found in the tendons of muscles and in the ear. The teeth are not
usually reckoned as separate bones, being a part of the structure of
the skin.
The number of distinct bones varies at different periods of life. It is
greater in childhood than in adults, for many bones which are then
separate, to allow growth, afterwards become gradually united. In early
adult life, for instance, the skull contains 22 naturally separate
bones, but in infancy the number is much greater, and in old age far
less.
The bones of the body thus arranged give firmness, strength, and
protection to the soft tissues and vital organs, and also form levers
for the muscles to act upon.
28. Chemical Composition of Bone. The bones, thus forming the framework
of the body, are hard, tough, and elastic. They are twice as strong as
oak; one cubic inch of compact bone will support a weight of 5000
pounds. Bone is composed of earthy or mineral matter (chiefly in the
form of lime salts), and of animal matter (principally gelatine), in
the proportion of two-thirds of the former to one-third of the latter.
Illustration: Fig. 10.—The Skeleton.
The proportion of earthy to animal matter varies with age. In infancy
the bones are composed almost wholly of animal matter. Hence, an
infant’s bones are rarely broken, but its legs may soon become
misshapen if walking is allowed too early. In childhood, the bones
still contain a larger percentage of animal matter than in more
advanced life, and are therefore more liable to bend than to break;
while in old age, they contain a greater percentage of mineral matter,
and are brittle and easily broken.
Experiment 3. _To show the mineral matter in bone_. Weigh a large soup
bone; put it on a hot, clear fire until it is at a red heat. At first
it becomes black from the carbon of its organic matter, but at last it
turns white. Let it cool and weigh again. The animal matter has been
burnt out, leaving the mineral or earthy part, a white, brittle
substance of exactly the same shape, but weighing only about two-thirds
as much as the bone originally weighed.
Experiment 4. _To show the animal matter in bone_. Add a teaspoonful of
muriatic acid to a pint of water, and place the mixture in a shallow
earthen dish. Scrape and clean a chicken’s leg bone, part of a sheep’s
rib, or any other small, thin bone. Soak the bone in the acid mixture
for a few days. The earthy or mineral matter is slowly dissolved, and
the bone, although retaining its original form, loses its rigidity, and
becomes pliable, and so soft as to be readily cut. If the experiment be
carefully performed, a long, thin bone may even be tied into a knot.
Illustration: Fig. 11.—The fibula tied into a knot, after the hard
mineral matter has been dissolved by acid.
29. Physical Properties of Bone. If we take a leg bone of a sheep, or a
large end of beef shin bone, and saw it lengthwise in halves, we see
two distinct structures. There is a hard and compact tissue, like
ivory, forming the outside shell, and a spongy tissue inside having the
appearance of a beautiful lattice work. Hence this is called cancellous
tissue, and the gradual transition from one to the other is apparent.
It will also be seen that the shaft is a hollow cylinder, formed of
compact tissue, enclosing a cavity called the medullary canal, which is
filled with a pulpy, yellow fat called _marrow_. The marrow is richly
supplied with blood-vessels, which enter the cavity through small
openings in the compact tissue. In fact, all over the surface of bone
are minute canals leading into the substance. One of these, especially
constant and large in many bones, is called the _nutrient foramen_, and
transmits an artery to nourish the bone.
At the ends of a long bone, where it expands, there is no medullary
canal, and the bony tissue is spongy, with only a thin layer of dense
bone around it. In flat bones we find two layers or plates of compact
tissue at the surface, and a spongy tissue between. Short and irregular
bones have no medullary canal, only a thin shell of dense bone filled
with cancellous tissue.
Illustration: Fig. 12.—The Right femur sawed in two, lengthwise.
(Showing arrangement of compact and cancellous tissue.)
Experiment 5. Obtain a part of a beef shin bone, or a portion of a
sheep’s or calf’s leg, including if convenient the knee joint. Have the
bone sawed in two, lengthwise, keeping the marrow in place. Boil,
scrape, and carefully clean one half. Note the compact and spongy
parts, shaft, etc.
Experiment 6. Trim off the flesh from the second half. Note the pinkish
white appearance of the bone, the marrow, and the tiny specks of blood,
etc. Knead a small piece of the marrow in the palm; note the oily
appearance. Convert some marrow into a liquid by heating. Contrast this
fresh bone with an old dry one, as found in the fields. Fresh bones
should be kept in a cool place, carefully wrapped in a damp cloth,
while waiting for class use.
A fresh or living bone is covered with a delicate, tough, fibrous
membrane, called the periosteum. It adheres very closely to the bone,
and covers every part except at the joints and where it is protected
with cartilage. The periosteum is richly supplied with blood-vessels,
and plays a chief part in the growth, formation, and repair of bone. If
a portion of the periosteum be detached by injury or disease, there is
risk that a layer of the subjacent bone will lose its vitality and be
cast off.[5]
30. Microscopic Structure of Bone. If a very thin slice of bone be cut
from the compact tissue and examined under a microscope, numerous
minute openings are seen. Around these are arranged rings of bone, with
little black bodies in them, from which radiate fine, dark lines. These
openings are sections of canals called _Haversian canals_, after
Havers, an English physician, who first discovered them. The black
bodies are minute cavities called _lacunæ_, while the fine lines are
very minute canals, _canaliculi_, which connect the lacunæ and the
Haversian canals. These Haversian canals are supplied with tiny
blood-vessels, while the lacunæ contain bone cells. Very fine branches
from these cells pass into the canaliculi. The Haversian canals run
lengthwise of the bone; hence if the bone be divided longitudinally
these canals will be opened along their length (Fig. 13).
Thus bones are not dry, lifeless substances, but are the very type of
activity and change. In life they are richly supplied with blood from
the nutrient artery and from the periosteum, by an endless network of
nourishing canals throughout their whole structure. Bone has,
therefore, like all other living structures, a _self-formative_ power,
and draws from the blood the materials for its own nutrition.
Illustration: Fig. 13.
A, longitudinal section of bone, by which the Haversian canals are
seen branching and communicating with one another;
B, cross section of a very thin slice of bone, magnified about 300
diameters—little openings (Haversian canals) are seen, and around
them are ranged rings of bones with little black bodies (lacunæ),
from which branch out fine dark lines (canaliculi);
C, a bone cell, highly magnified, lying in lacuna.
The Bones of the Head.
31. The Head, or Skull. The bones of the skeleton, the bony framework
of our bodies, may be divided into those of the head, the trunk, and
the limbs.
The bones of the head are described in two parts,—those of the cranium,
or brain-case, and those of the face. Taken together, they form the
skull. The head is usually said to contain 22 bones, of which 8 belong
to the cranium and 14 to the face. In early childhood, the bones of the
head are separate to allow the brain to expand; but as we grow older
they gradually unite, the better to protect the delicate brain tissue.
32. The Cranium. The cranium is a dome-like structure, made up in the
adult of 8 distinct bones firmly locked together. These bones are:
One Frontal,
Two Parietal,
Two Temporal
One Occipital,
One Sphenoid,
One Ethmoid.
The frontal bone forms the forehead and front of the head. It is united
with the two parietal bones behind, and extends over the forehead to
make the roofs of the sockets of the eyes. It is this bone which, in
many races of man, gives a dignity of person and a beauty of form seen
in no other animal.
The parietal bones form the sides and roof of the skull. They are
bounded anteriorly by the frontal bone, posteriorly by the occipital,
and laterally by the temporal and sphenoid bones. The two bones make a
beautiful arch to aid in the protection of the brain.
The temporal bones, forming the temples on either side, are attached to
the sphenoid bone in front, the parietals above, and the occipital
behind. In each temporal bone is the cavity containing the organs of
hearing. These bones are so called because the hair usually first turns
gray over them.
The occipital bone forms the lower part of the base of the skull, as
well as the back of the head. It is a broad, curved bone, and rests on
the topmost vertebra (atlas) of the backbone; its lower part is pierced
by a large oval opening called the _foramen magnum_, through which the
spinal cord passes from the brain (Fig. 15).
The sphenoid bone is in front of the occipital, forming a part of the
base of the skull. It is wedged between the bones of the face and those
of the cranium, and locks together fourteen different bones. It bears a
remarkable resemblance to a bat with extended wings, and forms a series
of girders to the arches of the cranium.
The ethmoid bone is situated between the bones of the cranium and those
of the face, just at the root of the nose. It forms a part of the floor
of the cranium. It is a delicate, spongy bone, and is so called because
it is perforated with numerous holes like a sieve, through which the
nerves of smell pass from the brain to the nose.
Illustration: Fig. 14.—The Skull
33. The Face. The bones of the face serve, to a marked extent, in
giving form and expression to the human countenance. Upon these bones
depend, in a measure, the build of the forehead, the shape of the chin,
the size of the eyes, the prominence of the cheeks, the contour of the
nose, and other marks which are reflected in the beauty or ugliness of
the face.
The face is made up of fourteen bones which, with the exception of the
lower jaw, are, like those of the cranium, closely interlocked with
each other. By this union these bones help form a number of cavities
which contain most important and vital organs. The two deep, cup-like
sockets, called the orbits, contain the organs of sight. In the
cavities of the nose is located the sense of smell, while the buccal
cavity, or mouth, is the site of the sense of taste, and plays besides
an important part in the first act of digestion and in the function of
speech.
The bones of the face are:
Two Superior Maxillary,
Two Malar,
Two Nasal,
Two Lachrymal,
Two Palate,
Two Turbinated,
One Vomer,
One Lower Maxillary.
34. Bones of the Face. The superior maxillary or upper jawbones form a
part of the roof of the mouth and the entire floor of the orbits. In
them is fixed the upper set of teeth.
The malar or cheek bones are joined to the upper jawbones, and help
form the sockets of the eyes. They send an arch backwards to join the
temporal bones. These bones are remarkably thick and strong, and are
specially adapted to resist the injury to which this part of the face
is exposed.
The nasal or nose bones are two very small bones between the eye
sockets, which form the bridge of the nose. Very near these bones are
the two small lachrymal bones. These are placed in the inner angles of
the orbit, and in them are grooves in which lie the ducts through which
the tears flow from the eyes to the nose.
The palate bones are behind those of the upper jaw and with them form
the bony part of the roof of the mouth. The inferior turbinated are
spongy, scroll-like bones, which curve about within the nasal cavities
so as to increase the surface of the air passages of the nose.
The vomer serves as a thin and delicate partition between the two
cavities of the nose. It is so named from its resemblance to a
ploughshare.
Illustration: Fig. 15.—The Base of the Skull.
A, palate process of upper jawbone;
B, zygoma, forming zygomatic arch;
C, condyle for forming articulation with atlas;
D, foramen magnum;
E, occipital bone.
The longest bone in the face is the inferior maxillary, or lower jaw.
It has a horseshoe shape, and supports the lower set of teeth. It is
the only movable bone of the head, having a vertical and lateral motion
by means of a hinge joint with a part of the temporal bone.
35. Sutures of the Skull. Before leaving the head we must notice the
peculiar and admirable manner in which the edges of the bones of the
outer shell of the skull are joined together. These edges of the bones
resemble the teeth of a saw. In adult life these tooth-like edges fit
into each other and grow together, suggesting the dovetailed joints
used by the cabinet-maker. When united these serrated edges look almost
as if sewed together; hence their name, sutures. This manner of union
gives unity and strength to the skull.
In infants, the corners of the parietal bones do not yet meet, and the
throbbing of the brain may be seen and felt under these “soft spots,”
or _fontanelles_, as they are called. Hence a slight blow to a babe’s
head may cause serious injury to the brain (Fig. 14).
The Bones of the Trunk.
36. The Trunk. The trunk is that central part of the body which
supports the head and the upper pair of limbs. It divides itself into
an upper cavity, the thorax, or chest; and a lower cavity, the abdomen.
These two cavities are separated by a movable, muscular partition
called the diaphragm, or midriff (Figs. 9 and 49).
The bones of the trunk are variously related to each other, and some of
them become united during adult life into bony masses which at earlier
periods are quite distinct. For example, the sacrum is in early life
made up of five distinct bones which later unite into one.
The upper cavity, or chest, is a bony enclosure formed by the
breastbone, the ribs, and the spine. It contains the heart and the
lungs (Fig. 86).
The lower cavity, or abdomen, holds the stomach, liver, intestines,
spleen, kidneys, and some other organs (Fig. 59).
The bones of the trunk may be subdivided into those of the spine, the
ribs, and the hips.
The trunk includes 54 bones usually thus arranged:
Spinal Column, 26 bones:
7 Cervical Vertebræ.
12 Dorsal Vertebræ.
5 Lumbar Vertebræ.
1 Sacrum.
1 Coccyx.
Ribs, 24 bones:
14 True Ribs.
6 False Ribs.
4 Floating Ribs.
Sternum.
IV. Two Hip Bones.
V. Hyoid Bone.
37. The Spinal Column. The spinal column, or backbone, is a marvelous
piece of mechanism, combining offices which nothing short of perfection
in adaptation and arrangement could enable it to perform. It is the
central structure to which all the other parts of the skeleton are
adapted. It consists of numerous separate bones, called vertebræ. The
seven upper ones belong to the neck, and are called cervical vertebræ.
The next twelve are the dorsal vertebræ; these belong to the back and
support the ribs. The remaining five belong to the loins, and are
called lumbar vertebræ. On looking at the diagram of the backbone (Fig.
9) it will be seen that the vertebræ increase in size and strength
downward, because of the greater burden they have to bear, thus clearly
indicating that an erect position is the one natural to man.
Illustration: Fig. 16.—The Spinal Column.
This column supports the head, encloses and protects the spinal cord,
and forms the basis for the attachment of many muscles, especially
those which maintain the body in an erect position. Each vertebra has
an opening through its center, and the separate bones so rest, one upon
another, that these openings form a continuous canal from the head to
the lower part of the spine. The great nerve, known as the spinal cord,
extends from the cranium through the entire length of this canal. All
along the spinal column, and between each two adjoining bones, are
openings on each side, through which nerves pass out to be distributed
to various parts of the body.
Between the vertebræ are pads or cushions of cartilage. These act as
“buffers,” and serve to give the spine strength and elasticity and to
prevent friction of one bone on another. Each vertebra consists of a
body, the solid central portion, and a number of projections called
processes. Those which spring from the posterior of each arch are the
spinous processes. In the dorsal region they are plainly seen and felt
in thin persons.
The bones of the spinal column are arranged in three slight and
graceful curves. These curves not only give beauty and strength to the
bony framework of the body, but also assist in the formation of
cavities for important internal organs. This arrangement of elastic
pads between the vertebræ supplies the spine with so many elastic
springs, which serve to break the effect of shock to the brain and the
spinal cord from any sudden jar or injury.
The spinal column rests on a strong three-sided bone called the sacrum,
or sacred-bone, which is wedged in between the hip bones and forms the
keystone of the pelvis. Joined to the lower end of the sacrum is the
coccyx, or cuckoo-bone, a tapering series of little bones.
Experiment 7. Run the tips of the fingers briskly down the backbone,
and the spines of the vertebræ will be tipped with red so that they can
be readily counted. Have the model lean forward with the arms folded
across the chest; this will make the spines of the vertebræ more
prominent.
Experiment 8. _To illustrate the movement of torsion in the spine, or
its rotation round its own axis_. Sit upright, with the back and
shoulders well applied against the back of a chair. Note that the head
and neck can be turned as far as 60° or 70°. Now bend forwards, so as
to let the dorsal and lumbar vertebræ come into play, and the head can
be turned 30° more.
Experiment 9. _To show how the spinal vertebræ make a firm but flexible
column._ Take 24 hard rubber overcoat buttons, or the same number of
two-cent pieces, and pile them on top of each other. A thin layer of
soft putty may be put between the coins to represent the pads of
cartilage between the vertebræ. The most striking features of the
spinal column may be illustrated by this simple apparatus.
38. How the Head and Spine are Joined together. The head rests upon the
spinal column in a manner worthy of special notice. This consists in
the peculiar structure of the first two cervical vertebræ, known as the
axis and atlas. The atlas is named after the fabled giant who supported
the earth on his shoulders. This vertebra consists of a ring of bone,
having two cup-like sockets into which fit two bony projections arising
on either side of the great opening (_foramen magnum_) in the occipital
bone. The hinge joint thus formed allows the head to nod forward, while
ligaments prevent it from moving too far.
On the upper surface of the axis, the second vertebra, is a peg or
process, called the _odontoid process_ from its resemblance to a tooth.
This peg forms a pivot upon which the head with the atlas turns. It is
held in its place against the front inner surface of the atlas by a
band of strong ligaments, which also prevents it from pressing on the
delicate spinal cord. Thus, when we turn the head to the right or left,
the skull and the atlas move together, both rotating on the odontoid
process of the axis.
39. The Ribs and Sternum. The barrel-shaped framework of the chest is
in part composed of long, slender, curved bones called ribs. There are
twelve ribs on each side, which enclose and strengthen the chest; they
somewhat resemble the hoops of a barrel. They are connected in pairs
with the dorsal vertebræ behind.
The first seven pairs, counting from the neck, are called the _true_
ribs, and are joined by their own special cartilages directly to the
breastbone. The five lower pairs, called the _false_ ribs, are not
directly joined to the breastbone, but are connected, with the
exception of the last two, with each other and with the last true ribs
by cartilages. These elastic cartilages enable the chest to bear great
blows with impunity. A blow on the sternum is distributed over fourteen
elastic arches. The lowest two pairs of false ribs, are not joined even
by cartilages, but are quite free in front, and for this reason are
called _floating_ ribs.
The ribs are not horizontal, but slope downwards from the backbone, so
that when raised or depressed by the strong intercostal muscles, the
size of the chest is alternately increased or diminished. This movement
of the ribs is of the utmost importance in breathing (Fig. 91).
The sternum, or breastbone, is a long, flat, narrow bone forming the
middle front wall of the chest. It is connected with the ribs and with
the collar bones. In shape it somewhat resembles an ancient dagger.
40. The Hip Bones. Four immovable bones are joined together so as to
form at the lower extremity of the trunk a basin-like cavity called the
pelvis. These four bones are the sacrum and the coccyx, which have been
described, and the two hip bones.
Illustration: Fig. 17.—Thorax. (Anterior view.)
The hip bones are large, irregularly shaped bones, very firm and
strong, and are sometimes called the haunch bones or _ossa innominata_
(nameless bones). They are united to the sacrum behind and joined to
each other in front. On the outer side of each hip bone is a deep cup,
or socket, called the _acetabulum_, resembling an ancient vinegar cup,
into which fits the rounded head of the thigh bone. The bones of the
pelvis are supported like a bridge on the legs as pillars, and they in
turn contain the internal organs in the lower part of the trunk.
41. The Hyoid Bone. Under the lower jaw is a little horseshoe shaped
bone called the hyoid bone, because it is shaped like the Greek letter
upsilon (Υ). The root of the tongue is fastened to its bend, and the
larynx is hung from it as from a hook. When the neck is in its natural
position this bone can be plainly felt on a level with the lower jaw
and about one inch and a half behind it. It serves to keep open the top
of the larynx and for the attachment of the muscles, which move the
tongue. (See Fig. 46.) The hyoid bone, like the knee-pan, is not
connected with any other bone.
The Bones of the Upper Limbs.
42. The Upper Limbs. Each of the upper limbs consist of the upper arm,
the forearm, and the hand. These bones are classified as follows:
Upper Arm: Scapula, or shoulder-blade,
Clavicle, or collar bone,
Humerus, or arm bone,
Forearm: Ulna,
Radius,
Hand: 8 Carpal or wrist bones,
5 Metacarpal bones,
14 Phalanges, or finger bones,
making 32 bones in all.
43. The Upper Arm. The two bones of the shoulder, the scapula and the
clavicle, serve in man to attach the arm to the trunk. The scapula, or
shoulder-blade, is a flat, triangular bone, placed point downwards, and
lying on the upper and back part of the chest, over the ribs. It
consists of a broad, flat portion and a prominent ridge or _spine_. At
its outer angle it has a shallow cup known as the _glenoid cavity_.
Into this socket fits the rounded head of the humerus. The
shoulder-blade is attached to the trunk chiefly by muscles, and is
capable of extensive motion.
The clavicle, or collar bone, is a slender bone with a double curve
like an italic _f_, and extends from the outer angle of the
shoulder-blade to the top of the breastbone. It thus serves like the
keystone of an arch to hold the shoulder-blade firmly in its place, but
its chief use is to keep the shoulders wide apart, that the arm may
enjoy a freer range of motion. This bone is often broken by falls upon
the shoulder or arm.
The humerus is the strongest bone of the upper extremity. As already
mentioned, its rounded head fits into the socket of the shoulder-blade,
forming a ball-and-socket joint, which permits great freedom of motion.
The shoulder joint resembles what mechanics call a universal joint, for
there is no part of the body which cannot be touched by the hand.
Illustration: Fig. 18.—Left Scapula, or Shoulder-Blade.
When the shoulder is dislocated the head of the humerus has been forced
out of its socket. The lower end of the bone is grooved to help form a
hinge joint at the elbow with the bones of the forearm (Fig. 27).
44. The Forearm. The forearm contains two long bones, the ulna and the
radius. The ulna, so called because it forms the elbow, is the longer
and larger bone of the forearm, and is on the same side as the little
finger. It is connected with the humerus by a hinge joint at the elbow.
It is prevented from moving too far back by a hook-like projection
called the _olecranon process_, which makes the sharp point of the
elbow.
The radius is the shorter of the two bones of the forearm, and is on
the same side as the thumb. Its slender, upper end articulates with the
ulna and humerus; its lower end is enlarged and gives attachment in
part to the bones of the wrist. This bone radiates or turns on the
ulna, carrying the hand with it.
Experiment 10. Rest the forearm on a table, with the palm up (an
attitude called supination). The radius is on the outer side and
parallel with the ulna If now, without moving the elbow, we turn the
hand (pronation), as if to pick up something from the table, the radius
may be seen and felt crossing over the ulna, while the latter has not
moved.
Illustration: Fig. 19.—Left Clavicle, or Collar Bone. (Anterior
surface.)
45. The Hand. The hand is the executive or essential part of the upper
limb. Without it the arm would be almost useless. It consists of 27
separate bones, and is divided into three parts, the wrist, the palm,
and the fingers.
Illustration: Fig. 20.—Left Humerus. Fig. 21.—Left Radius and Ulna.
The carpus, or wrist, includes 8 short bones, arranged in two rows of
four each, so as to form a broad support for the hand. These bones are
closely packed, and tightly bound with ligaments which admit of ample
flexibility. Thus the wrist is much less liable to be broken than if it
were to consist of a single bone, while the elasticity from having the
eight bones movable on each other, neutralizes, to a great extent, a
shock caused by falling on the hands. Although each of the wrist bones
has a very limited mobility in relation to its neighbors, their
combination gives the hand that freedom of action upon the wrist, which
is manifest in countless examples of the most accurate and delicate
manipulation.
The metacarpal bones are the five long bones of the back of the hand.
They are attached to the wrist and to the finger bones, and may be
easily felt by pressing the fingers of one hand over the back of the
other. The metacarpal bones of the fingers have little freedom of
movement, while the thumb, unlike the others, is freely movable. We are
thus enabled to bring the thumb in opposition to each of the fingers, a
matter of the highest importance in manipulation. For this reason the
loss of the thumb disables the hand far more than the loss of either of
the fingers. This very significant opposition of the thumb to the
fingers, furnishing the complete grasp by the hand, is characteristic
of the human race, and is wanting in the hand of the ape, chimpanzee,
and ourang-outang.
The phalanges, or finger bones, are the fourteen small bones arranged
in three rows to form the fingers. Each finger has three bones; each
thumb, two.
The large number of bones in the hand not only affords every variety of
movement, but offers great resistance to blows or shocks. These bones
are united by strong but flexible ligaments. The hand is thus given
strength and flexibility, and enabled to accomplish the countless
movements so necessary to our well-being.
In brief, the hand is a marvel of precise and adapted mechanism,
capable not only of performing every variety of work and of expressing
many emotions of the mind, but of executing its orders with
inconceivable rapidity.
The Bones of the Lower Limbs.
46. The Lower Limbs. The general structure and number of the bones of
the lower limbs bear a striking similarity to those of the upper limbs.
Thus the leg, like the arm, is arranged in three parts, the thigh, the
lower leg, and the foot. The thigh bone corresponds to the humerus; the
tibia and fibula to the ulna and radius; the ankle to the wrist; and
the metatarsus and the phalanges of the foot, to the metacarpus and the
phalanges of the hand.
The bones of the lower limbs may be thus arranged:
Thigh: Femur, or thigh bone,
Lower Leg: Patella, or knee cap,
Tibia, or shin bone,
Fibula, or splint bone,
Foot: 7 Tarsal or ankle bones,
5 Metatarsal or instep bones,
14 Phalanges, or toes bones,
making 30 bones in all.
Illustration: Fig. 22.—Right Femur, or Thigh Bone.
47. The Thigh. The longest and strongest of all the bones is the femur,
or thigh bone. Its upper end has a rounded head which fits into the
_acetabulum_, or the deep cup-like cavity of the hip bone, forming a
perfect ball-and-socket joint. When covered with cartilage, the ball
fits so accurately into its socket that it may be retained by
atmospheric pressure alone (sec. 50).
The shaft of the femur is strong, and is ridged and roughened in places
for the attachment of the muscles. Its lower end is broad and
irregularly shaped, having two prominences called _condyles_, separated
by a groove, the whole fitted for forming a hinge joint with the bones
of the lower leg and the knee-cap.
48. The Lower Leg. The lower leg, like the forearm, consists of two
bones. The tibia, or shin bone, is the long three-sided bone forming
the front of the leg. The sharp edge of the bone is easily felt just
under the skin. It articulates with the lower end of the thigh bone,
forming with it a hinge joint.
The fibula, the companion bone of the tibia, is the long, slender bone
on the outer side of the leg. It is firmly fixed to the tibia at each
end, and is commonly spoken of as the small bone of the leg. Its lower
end forms the outer projection of the ankle. In front of the knee
joint, embedded in a thick, strong tendon, is an irregularly
disk-shaped bone, the patella, or knee-cap. It increases the leverage
of important muscles, and protects the front of the knee joint, which
is, from its position, much exposed to injury.
Illustration: Fig. 23.—Patella, or Knee-Cap.
49. The Foot. The bones of the foot, 26 in number, consist of the
tarsal bones, the metatarsal, and the phalanges. The tarsal bones are
the seven small, irregular bones which make up the ankle. These bones,
like those of the wrist, are compactly arranged, and are held firmly in
place by ligaments which allow a considerable amount of motion.
One of the ankle bones, the _os calcis_, projects prominently
backwards, forming the heel. An extensive surface is thus afforded for
the attachment of the strong tendon of the calf of the leg, called the
tendon of Achilles. The large bone above the heel bone, the
_astragalus_, articulates with the tibia, forming a hinge joint, and
receives the weight of the body.
The metatarsal bones, corresponding to the metacarpals of the hand, are
five in number, and form the lower instep.
The phalanges are the fourteen bones of the toes,—three in each except
the great toe, which, like the thumb, has two. They resemble in number
and plan the corresponding bones in the hand. The bones of the foot
form a double arch,—an arch from before backwards, and an arch from
side to side. The former is supported behind by the os calcis, and in
front by the ends of the metatarsal bones. The weight of the body falls
perpendicularly on the astragalus, which is the key-bone or crown of
the arch. The bones of the foot are kept in place by powerful
ligaments, combining great strength with elasticity.
Illustration: Fig. 24.—Right Tibia and Fibula (Anterior surface.)
Illustration: Fig. 25.—Bones of Right Foot. (Dorsal surface.)
The Joints.
50. Formation of Joints. The various bones of the skeleton are
connected together at different parts of their surfaces by joints, or
articulations. Many different kinds of joints have been described, but
the same general plan obtains for nearly all. They vary according to
the kind and the amount of motion.
The principal structures which unite in the formation of a joint are:
bone, cartilage, synovial membrane, and ligaments. Bones make the chief
element of all the joints, and their adjoining surfaces are shaped to
meet the special demands of each joint (Fig. 27). The joint-end of
bones is coated with a thin layer of tough, elastic cartilage. This is
also used at the edge of joint-cavities, forming a ring to deepen them.
The rounded heads of bones which move in them are thus more securely
held in their sockets.
Besides these structures, the muscles also help to maintain the
joint-surfaces in proper relation. Another essential to the action of
the joints is the pressure of the outside air. This may be sufficient
to keep the articular surfaces in contact even after all the muscles
are removed. Thus the hip joint is so completely surrounded by
ligaments as to be air-tight; and the union is very strong. But if the
ligaments be pierced and air allowed to enter the joint, the union at
once becomes much less close, and the head of the thigh bone falls away
as far as the ligaments will allow it.
51. Synovial Membrane. A very delicate connective tissue, called the
synovial membrane, lines the capsules of the joints, and covers the
ligaments connected with them. It secretes the _synovia_, or joint oil,
a thick and glairy fluid, like the white of a raw egg, which thoroughly
lubricates the inner surfaces of the joints. Thus the friction and heat
developed by movement are reduced, and every part of a joint is enabled
to act smoothly.
52. Ligaments. The bones are fastened together, held in place, and
their movements controlled, to a certain extent, by bands of various
forms, called ligaments. These are composed mainly of bundles of white
fibrous tissue placed parallel to, or closely interlaced with, one
another, and present a shining, silvery aspect. They extend from one of
the articulating bones to another, strongly supporting the joint, which
they sometimes completely envelope with a kind of cap (Fig. 28). This
prevents the bones from being easily dislocated. It is difficult, for
instance, to separate the two bones in a shoulder or leg of mutton,
they are so firmly held together by tough ligaments.
While ligaments are pliable and flexible, permitting free movement,
they are also wonderfully strong and inextensible. A bone may be
broken, or its end torn off, before its ligaments can be ruptured. The
wrist end of the radius, for instance, is often torn off by force
exerted on its ligaments without their rupture.
The ligaments are so numerous and various and are in some parts so
interwoven with each other, that space does not allow even mention of
those that are important. At the knee joint, for instance, there are no
less than fifteen distinct ligaments.
53. Imperfect Joints. It is only perfect joints that are fully equipped
with the structures just mentioned. Some joints lack one or more, and
are therefore called imperfect joints. Such joints allow little or no
motion and have no smooth cartilages at their edges. Thus, the bones of
the skull are dovetailed by joints called sutures, which are immovable.
The union between the vertebræ affords a good example of imperfect
joints which are partially movable.
Illustration: Fig. 26.—Elastic Tissue from the Ligaments about Joints.
(Highly magnified.)
54. Perfect Joints. There are various forms of perfect joints,
according to the nature and amount of movement permitted. They an
divided into hinge joints, ball-and-socket joints and pivot joints.
The hinge joints allow forward and backward movements like a hinge.
These joints are the most numerous in the body, as the elbow, the
ankle, and the knee joints.
In the ball-and-socket joints—a beautiful contrivance—the rounded head
of one bone fits into a socket in the other, as the hip joint and
shoulder joint. These joints permit free motion in almost every
direction.
In the pivot joint a kind of peg in one bone fits into a notch in
another. The best example of this is the joint between the first and
second vertebræ (see sec. 38). The radius moves around on the ulna by
means of a pivot joint. The radius, as well as the bones of the wrist
and hand, turns around, thus enabling us to turn the palm of the hand
upwards and downwards. In many joints the extent of motion amounts to
only a slight gliding between the ends of the bones.
55. Uses of the Bones. The bones serve many important and useful
purposes. The skeleton, a general framework, affords protection,
support, and leverage to the bodily tissues. Thus, the bones of the
skull and of the chest protect the brain, the lungs, and the heart; the
bones of the legs support the weight of the body; and the long bones of
the limbs are levers to which muscles are attached.
Owing to the various duties they have to perform, the bones are
constructed in many different shapes. Some are broad and flat; others,
long and cylindrical; and a large number very irregular in form. Each
bone is not only different from all the others, but is also curiously
adapted to its particular place and use.
Illustration: Fig. 27.—Showing how the Ends of the Bones are shaped to
form the Elbow Joint. (The cut ends of a few ligaments are seen.)
Nothing could be more admirable than the mechanism by which each one of
the bones is enabled to fulfill the manifold purposes for which it was
designed. We have seen how the bones of the cranium are united by
sutures in a manner the better to allow the delicate brain to grow, and
to afford it protection from violence. The arched arrangement of the
bones of the foot has several mechanical advantages, the most important
being that it gives firmness and elasticity to the foot, which thus
serves as a support for the weight of the body, and as the chief
instrument of locomotion.
The complicated organ of hearing is protected by a winding series of
minute apartments, in the rock-like portion of the temporal bone. The
socket for the eye has a jutting ridge of bone all around it, to guard
the organ of vision against injury. Grooves and canals, formed in hard
bone, lodge and protect minute nerves and tiny blood-vessels. The
surfaces of bones are often provided with grooves, sharp edges, and
rough projections, for the origin and insertion of muscles.
Illustration: Fig. 28.—External Ligaments of the Knee.
56. The Bones in Infancy and Childhood. The bones of the infant,
consisting almost wholly of cartilage, are not stiff and hard as in
after life, but flexible and elastic. As the child grows, the bones
become more solid and firmer from a gradually increased deposit of lime
salts. In time they become capable of supporting the body and
sustaining the action of the muscles. The reason is that well-developed
bones would be of no use to a child that had not muscular strength to
support its body. Again, the numerous falls and tumbles that the child
sustains before it is able to walk, would result in broken bones almost
every day of its life. As it is, young children meet with a great
variety of falls without serious injury.
But this condition of things has its dangers. The fact that a child’s
bones bend easily, also renders them liable to permanent change of
shape. Thus, children often become bow-legged when allowed to walk too
early. Moderate exercise, however, even in infancy, promotes the health
of the bones as well as of the other tissues. Hence a child may be kept
too long in its cradle, or wheeled about too much in a carriage, when
the full use of its limbs would furnish proper exercise and enable it
to walk earlier.
57. Positions at School. Great care must be exercised by teachers that
children do not form the habit of taking injurious positions at school.
The desks should not be too low, causing a forward stoop; or too high,
throwing one shoulder up and giving a twist to the spine. If the seats
are too low there will result an undue strain on the shoulder and the
backbone; if too high, the feet have no proper support, the thighs may
be bent by the weight of the feet and legs, and there is a prolonged
strain on the hips and back. Curvature of the spine and round shoulders
often result from long-continued positions at school in seats and at
desks which are not adapted to the physical build of the occupant.
Illustration: Fig. 29.—Section of the Knee Joint. (Showing its internal
structure)
A, tendon of the semi-membranosus muscle cut across;
B, F, tendon of same muscle;
C, internal condyle of femur;
D, posterior crucial ligament;
E, internal interarticular fibro cartilage;
G, bursa under knee-cap;
H, ligament of knee-cap;
K, fatty mass under knee-cap;
L, anterior crucial ligament cut across;
P, patella, or knee-cap
A few simple rules should guide teachers and school officials in
providing proper furniture for pupils. Seats should be regulated
according to the size and age of the pupils, and frequent changes of
seats should be made. At least three sizes of desks should be used in
every schoolroom, and more in ungraded schools. The feet of each pupil
should rest firmly on the floor, and the edge of the desk should be
about one inch higher than the level of the elbows. A line dropped from
the edge of the desk should strike the front edge of the seat. Sliding
down into the seat, bending too much over the desk while writing and
studying, sitting on one foot or resting on the small of the back, are
all ungraceful and unhealthful positions, and are often taken by pupils
old enough to know better. This topic is well worth the vigilance of
every thoughtful teacher, especially of one in the lower grades.
58. The Bones in After Life. Popular impression attributes a less share
of life, or a lower grade of vitality, to the bones than to any other
part of the body. But really they have their own circulation and
nutrition, and even nervous relations. Thus, bones are the seat of
active vital processes, not only during childhood, but also in adult
life, and in fact throughout life, except perhaps in extreme old age.
The final knitting together of the ends of some of the bones with their
shafts does not occur until somewhat late in life. For example, the
upper end of the tibia and its shaft do not unite until the
twenty-first year. The separate bones of the sacrum do not fully knit
into one solid bone until the twenty-fifth year. Hence, the risk of
subjecting the bones of young persons to undue violence from
injudicious physical exercise as in rowing, baseball, football, and
bicycle-riding.
The bones during life are constantly going through the process of
absorption and reconstruction. They are easily modified in their
growth. Thus the continued pressure of some morbid deposit, as a tumor
or cancer, or an enlargement of an artery, may cause the absorption or
distortion of bones as readily as of one of the softer tissues. The
distortion resulting from tight lacing is a familiar illustration of
the facility with which the bones may be modified by prolonged
pressure.
Some savage races, not content with the natural shape of the head, take
special methods to mould it by continued artificial pressure, so that
it may conform in its distortion to the fashion of their tribe or race.
This custom is one of the most ancient and widespread with which we are
acquainted. In some cases the skull is flattened, as seen in certain
Indian tribes on our Pacific coast, while with other tribes on the same
coast it is compressed into a sort of conical appearance. In such cases
the brain is compelled, of course, to accommodate itself to the change
in the shape of the head; and this is done, it is said, without any
serious result.
59. Sprains and Dislocations. A twist or strain of the ligaments and
soft parts about a joint is known as a sprain, and may result from a
great variety of accidents. When a person falls, the foot is frequently
caught under him, and the twist comes upon the ligaments and tissues of
the ankle. The ligaments cannot stretch, and so have to endure the
wrench upon the joint. The result is a sprained ankle. Next to the
ankle, a sprain of the wrist is most common. A person tries, by
throwing out his hand, to save himself from a fall, and the weight of
the body brings the strain upon the firmly fixed wrist. As a result of
a sprain, the ligaments may be wrenched or torn, and even a piece of an
adjacent bone may be torn off; the soft parts about the injured joint
are bruised, and the neighboring muscles put to a severe stretch. A
sprain may be a slight affair, needing only a brief rest, or it may be
severe and painful enough to call for the most skillful treatment by a
surgeon. Lack of proper care in severe sprains often results in
permanent lameness.
A fall or a blow may bring such a sudden wrench or twist upon the
ligaments as to force a bone out of place. This displacement is known
as a dislocation. A child may trip or fall during play and put his
elbow out of joint. A fall from horseback, a carriage, or a bicycle may
result in a dislocation of the shoulder joint. In playing baseball a
swift ball often knocks a finger out of joint. A dislocation must be
reduced at once. Any delay or carelessness may make a serious and
painful affair of it, as the torn and bruised parts rapidly swell and
become extremely sensitive.
60. Broken Bones. The bones, especially those of the upper limbs, are
often fractured or broken. The _simple_ fracture is the most common
form, the bone being broken in a single place with no opening through
the skin. When properly adjusted, the bone heals rapidly. Sometimes
bones are crushed into a number of fragments; this is a _comminuted_
fracture. When, besides the break, there is an opening through the soft
parts and surface of the body, we have a _compound_ fracture. This is a
serious injury, and calls for the best surgical treatment.
A bone may be bent, or only partly broken, or split. This is called “a
green-stick fracture,” from its resemblance to a half-broken green
stick. This fracture is more common in the bones of children.
Fractures may be caused by direct violence, as when a bone is broken at
a certain point by some powerful force, as a blow from a baseball bat
or a fall from a horse. Again, a bone may be broken by indirect
violence, as when a person being about to fall, throws out his hand to
save himself. The force of the fall on the hand often breaks the wrist,
by which is meant the fracture of the lower end of the radius, often
known as the “silver-fork fracture.” This accident is common in winter
from a fall or slip on the ice.
Sometimes bones are broken at a distance from the point of injury, as
in a fracture of the ribs by violent compression of the chest; or
fracture may occur from the vibration of a blow, as when a fall or blow
upon the top of the head produces fracture of the bones at the base of
the brain.[6]
61. Treatment for Broken Bones. When a bone is broken a surgeon is
needed to set it, that is, to bring the broken parts into their natural
position, and retain them by proper appliances. Nature throws out
between and around the broken ends of bones a supply of repair material
known as plastic lymph, which is changed to fibrous tissue, then to
cartilage, and finally to bone. This material serves as a sort of
cement to hold the fractured parts together. The excess of this at the
point of union can be felt under the skin for some time after the bone
is healed.
With old people a broken bone is often a serious matter, and may
cripple them for life or prove fatal. A trifling fall, for instance,
may cause a broken hip (popularly so called, though really a fracture
of the neck of the femur), from the shock of which, and the subsequent
pain and exhaustion, an aged person may die in a few weeks. In young
people, however, the parts of a broken bone will knit together in three
or four weeks after the fracture is reduced; while in adults, six or
even more may be required for firm union. After a broken bone is strong
enough to be used, it is fragile for some time; and great care must be
taken, especially with children, that the injured parts may not be
broken again before perfect union takes place.[7]
62. The Effect of Alcohol upon the Bones. While the growth of the bones
occurs, of course, mainly during the earlier years of life, yet they do
not attain their full maturity until about the twenty-fifth year; and
it is stated that in persons devoted to intellectual pursuits, the
skull grows even after that age. It is plainly necessary that during
this period of bone growth the nutrition of the body should be of the
best, that the bones may be built up from pure blood, and supplied with
all the materials for a large and durable framework. Else the body will
be feeble and stunted, and so through life fall short of its purpose.
If this bony foundation be then laid wrong, the defect can never be
remedied. This condition is seen in young persons who have been
underfed and overworked. But the use of alcoholic liquors produces a
similar effect, hindering bone cell-growth and preventing full
development.[8] The appetite is diminished, nutrition perverted and
impaired, the stature stunted, and both bodily and mental powers are
enfeebled.
63. Effect of Tobacco upon the Bones. Another narcotic, the destructive
influence of which is wide and serious, is tobacco. Its pernicious
influence, like that of alcohol, is peculiarly hurtful to the young, as
the cell development during the years of growth is easily disturbed by
noxious agents. The bone growth is by cells, and a powerful narcotic
like tobacco retards cell-growth, and thus hinders the building up of
the bodily frame. The formation of healthy bone demands good,
nutritious blood, but if instead of this, the material furnished for
the production of blood is poor in quality or loaded with poisonous
narcotics, the body thus defrauded of its proper building material
becomes undergrown and enfeebled.
Two unfavorable facts accompany this serious drawback: one is, that
owing to the insidious nature of the smoky poison[9] (cigarettes are
its worst form) the cause may often be unsuspected, and so go on,
unchecked; and the other, that the progress of growth once interrupted,
the gap can never be fully made up. Nature does her best to repair
damages and to restore defects, but never goes backwards to remedy
neglects.
Additional Experiments.
Experiment 11. Take a portion of the decalcified bone obtained from
Experiment 4, and wash it thoroughly in water: in this it is insoluble.
Place it in a solution of carbonate of soda and wash it again. Boil it
in water, and from it gelatine will be obtained.
Experiment 12. Dissolve in hydrochloric acid a small piece of the
powdered bone-ash obtained from Experiment 3. Bubbles of carbon dioxid
are given off, indicating the presence of a carbonate. Dilute the
solution; add an excess of ammonia, and we find a white precipitate of
the phosphate of lime and of magnesia.
Experiment 13. Filter the solution in the preceding experiment, and to
the filtrate add oxalate of ammonia. The result is a white precipitate
of the oxalate of lime, showing there is lime present, but not as a
phosphate.
Experiment 14. To the solution of mineral matters obtained from
Experiment 3, add acetate of soda until free acetic acid is present,
recognized by the smell (like dilute vinegar); then add oxalate of
ammonia. The result will be a copious white precipitate of lime salts.
Experiment 15. _To show how the cancellous structure of bone is able to
support a great deal of weight_. Have the market-man saw out a cubic
inch from the cancellous tissue of a fresh beef bone and place it on a
table with its principal layers upright. Balance a heavy book upon it,
and then gradually place upon it various articles and note how many
pounds it will support before giving way.
Experiment 16. Repeat the last experiment, using a cube of the
decalcified bone obtained from Experiment 4.
Note. As the succeeding chapters are studied, additional experiments on
bones and their relation to other parts of the body, will readily
suggest themselves to the ingenious instructor or the thoughtful
student. Such experiments may be utilized for review or other
exercises.
Review Analysis: The Skeleton (206 bones).
/ / 1 Frontal,
/ / 2 Parietal,
/ I. Cranium | 2 Temporal,
/ (8 bones) | 1 Occipital,
/ \ 1 Sphenoid,
| \ 1 Ethmoid.
|
| / 2 Superior Maxillary,
The Head | / 2 Malar,
(28 bones). | / 2 Nasal,
| II. Face | 2 Lachrymal Bones,
| (14 bones) | 2 Palate Bones,
| \ 2 Turbinated,
| \ 1 Vomer,
\ \ 1 Lower Maxillary.
\
\ / Hammer,
\ III. The Ear | Anvil,
\ (6 bones) \ Stirrup.
/ / 7 Cervical Vertebræ.
/ / 12 Dorsal Vertebræ,
/ I. Spinal Column | 5 Lumbar Vertebræ,
| (26 bones) \ Sacrum,
| \ Coccyx.
The Trunk |
(54 bones). | / 7 True Ribs,
| II. The Ribs | 3 False Ribs,
| (24 bones) \ 2 Floating Ribs.
|
\ III. Sternum.
\ IV. Two Hip Bones.
\ V. Hyoid Bone.
/ / Scapula,
/ I. Upper Arm | Clavicle,
| \ Humerus.
|
The Upper Limbs | II. Forearm / Ulna,
(64 bones). | \ Radius.
|
| / 8 Carpal Bones,
\ III. Hand | 5 Metacarpal Bones,
\ \ 14 Phalanges.
/ I. Thigh Femur.
/
| / Patella,
The Lower Limbs | II. Lower Leg | Tibia,
(60 bones). | \ Fibula.
|
| / 7 Tarsal Bones,
\ III. Foot | 5 Metatarsal Bones,
\ \ 14 Phalanges.
Chapter III.
The Muscles.
64. Motion in Animals. All motion of our bodies is produced by means of
muscles. Not only the limbs are moved by them, but even the movements
of the stomach and of the heart are controlled by muscles. Every part
of the body which is capable of motion has its own special set of
muscles.
Even when the higher animals are at rest it is possible to observe some
kind of motion in them. Trees and stones never move unless acted upon
by external force, while the infant and the tiniest insect can execute
a great variety of movements. Even in the deepest sleep the beating of
the heart and the motion of the chest never cease. In fact, the power
to execute spontaneous movement is the most characteristic property of
living animals.
65. Kinds of Muscles. Most of the bodily movements, such as affect the
limbs and the body as a whole, are performed by muscles under our
control. These muscles make up the red flesh or lean parts, which,
together with the fat, clothe the bony framework, and give to it
general form and proportion. We call these muscular tissues voluntary
muscles, because they usually act under the control of the will.
The internal organs, as those of digestion, secretion, circulation, and
respiration, perform their functions by means of muscular activity of
another kind, that is, by that of muscles not under our control. This
work goes on quite independently of the will, and during sleep. We call
the instruments of this activity involuntary muscles. The voluntary
muscles, from peculiarities revealed by the microscope, are also known
as striped or striated muscles. The involuntary from their smooth,
regular appearance under the microscope are called the unstriped or
non-striated muscles.
The two kinds of muscles, then, are the red, voluntary, striated
muscles, and the smooth, involuntary, non-striated muscles.
66. Structure of Voluntary Muscles. The main substance which clothes
the bony framework of the body, and which forms about two-fifths of its
weight, is the voluntary muscular tissue. These muscles do not cover
and surround the bones in continuous sheets, but consist of separate
bundles of flesh, varying in size and length, many of which are capable
of independent movement.
Each muscle has its own set of blood-vessels, lymphatics, and nerves.
It is the blood that gives the red color to the flesh. Blood-vessels
and nerves on their way to other parts of the body, do not pass through
the muscles, but between them. Each muscle is enveloped in its own
sheath of connective tissue, known as the fascia. Muscles are not
usually connected directly with bones, but by means of white,
glistening cords called tendons.
Illustration: Fig. 30.—Striated (voluntary) Muscular Fibers.
A, fiber serparating into disks;
B, fibrillæ (highly magnified);
C, cross section of a disk
If a small piece of muscle be examined under a microscope it is found
to be made up of bundles of fibers. Each fiber is enclosed within a
delicate, transparent sheath, known as the sarcolemma. If one of these
fibers be further examined under a microscope, it will be seen to
consist of a great number of still more minute fibers called fibrillæ.
These fibers are also seen marked cross-wise with dark stripes, and can
be separated at each stripe into disks. These cross markings account
for the name _striped_ or _striated_ muscle.
The fibrillæ, then, are bound together in a bundle to form a fiber,
which is enveloped in its own sheath, the sarcolemma. These fibers, in
turn, are further bound together to form larger bundles called
fasciculi, and these, too, are enclosed in a sheath of connective
tissue. The muscle itself is made up of a number of these fasciculi
bound together by a denser layer of connective tissue.
Experiment 17. _To show the gross structure of muscle._ Take a small
portion of a large muscle, as a strip of lean corned beef. Have it
boiled until its fibers can be easily separated. Pick the bundles and
fasciculi apart until the fibers are so fine as to be almost invisible
to the naked eye. Continue the experiment with the help of a hand
magnifying glass or a microscope.
67. The Involuntary Muscles. These muscles consist of ribbon-shaped
bands which surround hollow fleshy tubes or cavities. We might compare
them to India rubber rings on rolls of paper. As they are never
attached to bony levers, they have no need of tendons.
Illustration: Fig. 31.—A, Muscular Fiber, showing Stripes, and Nuclei,
b and c. (Highly magnified.)
The microscope shows these muscles to consist not of fibers, but of
long spindle-shaped cells, united to form sheets or bands. They have no
sarcolemma, stripes, or cross markings like those of the voluntary
muscles. Hence their name of _non-striated_, or _unstriped_, and
_smooth_ muscles.
The involuntary muscles respond to irritation much less rapidly than do
the voluntary. The wave of contraction passes over them more slowly and
more irregularly, one part contracting while another is relaxing. This
may readily be seen in the muscular action of the intestines, called
vermicular motion. It is the irregular and excessive contraction of the
muscular walls of the bowels that produces the cramp-like pains of
colic.
The smooth muscles are found in the tissues of the heart, lungs,
blood-vessels, stomach, and intestines. In the stomach their
contraction produces the motion by which the food is churned about; in
the arteries and veins they help supply the force by which the blood is
driven along, and in the intestines that by which the partly digested
food is mainly kept in motion.
Thus all the great vital functions are carried on, regardless of the
will of the individual, or of any outward circumstances. If it required
an effort of the will to control the action of the internal organs we
could not think of anything else. It would take all our time to attend
to living. Hence the care of such delicate and important machinery has
wisely been put beyond our control.
Thus, too, these muscles act instinctively without training; but the
voluntary need long and careful education. A babe can use the muscles
of swallowing on the first day of its life as well as it ever can. But
as it grows up, long and patient education of its voluntary muscles is
needed to achieve walking, writing, use of musical instruments, and
many other acts of daily life.
Illustration: Fig. 32.—A Spindle Cell of Involuntary Muscle. (Highly
magnified.)
Experiment 18. _To show the general appearance of the muscles._ Obtain
the lower part of a sheep’s or calf’s leg, with the most of the lean
meat and the hoof left on. One or more of the muscles with their
bundles of fibers, fascia, and tendons; are readily made out with a
little careful dissection. The dissection should be made a few days
before it is wanted and the parts allowed to harden somewhat in dilute
alcohol.
68. Properties of Muscular Tissue. The peculiar property of living
muscular tissue is irritability, or the capacity of responding to a
stimulus. When a muscle is irritated it responds by contracting. By
this act the muscle does not diminish its bulk to any extent; it simply
changes its form. The ends of the muscle are drawn nearer each other
and the middle is thicker.
Muscles do not shorten themselves all at once, but the contraction
passes quickly over them in the form of a wave. They are usually
stimulated by nervous action. The delicate nerve fibrils which end in
the fibers communicate with the brain, the center of the will power.
Hence, when the brain commands, a nervous impulse, sent along the nerve
fibers, becomes the exciting stimulus which acts upon the muscles and
makes them shorter, harder, and more rigid.[10]
Muscles, however, will respond to other than this usual stimulus. Thus
an electrical current may have a similar effect. Heat, also, may
produce muscular contraction. Mechanical means, such as a sharp blow or
pinching, may irritate a muscle and cause it to contract.
We must remember that this property of contraction is inherent and
belongs to the muscle itself. This power of contraction is often
independent of the brain. Thus, on pricking the heart of a fish an hour
after removal from its body, obvious contraction will occur. In this
case it is not the nerve force from the brain that supplies the energy
for contraction. The power of contraction is inherent in the muscle
substance, and the stimulus by irritating the nerve ganglia of the
heart simply affords the opportunity for its exercise.
Contraction is not, however, the natural state of a muscle. In time it
is tired, and begins to relax. Even the heart, the hardest-working
muscle, has short periods of rest between its beats. Muscles are highly
elastic as well as contractile. By this property muscle yields to a
stretching force, and returns to its original length if the stretching
has not been excessive.
Illustration: Fig. 33.—Principal Muscles of the Body. (Anterior view.)
69. The Object of Contraction. The object of contraction is obvious.
Like rubber bands, if one end of a muscle be fixed and the other
attached to some object which is free to move, the contraction of the
muscle will bring the movable body nearer to the fixed point. A weight
fastened to the free end of a muscle may be lifted when the muscle
contracts. Thus by their contraction muscles are able to do their work.
They even contract more vigorously when resistance is opposed to them
than when it is not. With increased weight there is an increased amount
of work to be done. The greater resistance calls forth a greater action
of the muscle. This is true up to a certain point, but when the limit
has been passed, the muscle quickly fails to respond.
Again, muscles work best with a certain degree of rapidity provided the
irritations do not follow each other too rapidly. If, however, the
contractions are too rapid, the muscles become exhausted and fatigue
results. When the feeling of fatigue passes away with rest, the muscle
recovers its power. While we are resting, the blood is pouring in fresh
supplies of building material.
Experiment 19. _To show how muscles relax and contract_. Lay your left
forearm on a table; grasp with the right hand the mass of flesh on the
front of the upper arm. Now gradually raise the forearm, keeping the
elbow on the table. Note that the muscle thickens as the hand rises.
This illustrates the contraction of the biceps, and is popularly called
“trying your muscle” Reverse the act. Keep the elbow in position, bring
the forearm slowly to the table, and the biceps appears to become
softer and smaller,—it relaxes.
Experiment 20. Repeat the same experiment with other muscles. With the
right hand grasp firmly the extended left forearm. Extend and flex the
fingers vigorously. Note the effect on the muscles and tendons of the
forearm. Grasp with the right hand the calf of the extended right leg,
and vigorously flex the leg, bringing it near to the body. Note the
contractions and relaxations of the muscles.
70. Arrangement of Muscles. Muscles are not connected directly with
bones. The mass of flesh tapers off towards the ends, where the fibers
pass into white, glistening cords known as tendons. The place at which
a muscle is attached to a bone, generally by means of a tendon, is
called its origin; the end connected with the movable bone is its
insertion.
There are about 400 muscles in the human body, all necessary for its
various movements. They vary greatly in shape and size, according to
their position and use. Some are from one to two feet long, others only
a fraction of an inch. Some are long and spindle-shaped, others thin
and broad, while still others form rings. Thus some of the muscles of
the arm and thigh are long and tapering, while the abdominal muscles
are thin and broad because they help form walls for cavities. Again,
the muscular fibers which surround and by their contraction close
certain orifices, as those of the eyelids and lips, often radiate like
the spokes of a wheel.
Muscles are named according to their shape, position, division of
origin or insertion, and their function. Thus we have the _recti_
(straight), and the _deltoid_ (Δ, delta), the _brachial_ (arm),
_pectoral_ (breast), and the _intercostals_ (between the ribs), so
named from their position. Again, we have the _biceps_ (two-headed),
_triceps_ (three-headed), and many others with similar names, so called
from the points of origin and insertion. We find other groups named
after their special use. The muscles which bend the limbs are called
_flexors_ while those which straighten them are known as _extensors_.
After a bone has been moved by the contraction of a muscle, it is
brought back to its position by the contraction of another muscle on
the opposite side, the former muscle meanwhile being relaxed. Muscles
thus acting in opposition to each other are called antagonistic. Thus
the biceps serves as one of the antagonists to the triceps, and the
various flexors and extensors of the limbs are antagonistic to one
another.
71. The Tendons. The muscles which move the bones by their contraction
taper for the most part, as before mentioned, into tendons. These are
commonly very strong cords, like belts or straps, made up of white,
fibrous tissue.
Tendons are most numerous about the larger joints, where they permit
free action and yet occupy but little space. Large and prominent
muscles in these places would be clumsy and inconvenient. If we bend
the arm or leg forcibly, and grasp the inside of the elbow or knee
joint, we can feel the tendons beneath the skin. The numerous tendons
in the palm or on the back of the hand contribute to its marvelous
dexterity and flexibility. The thickest and strongest tendon in the
body is the tendon of Achilles, which connects the great muscles in the
calf of the leg with the heel bone (sec. 49).
When muscles contract forcibly, they pull upon the tendons which
transmit the movement to the bones to which they are attached. Tendons
may be compared to ropes or cords which, when pulled, are made to act
upon distant objects to which one end is fastened. Sometimes the tendon
runs down the middle of a muscle, and the fibers run obliquely into it,
the tendon resembling the quill in a feather. Again, tendons are spread
out in a flat layer on the surface of muscles, in which case they are
called aponeuroses. Sometimes a tendon is found in the middle of a
muscle as well as at each end of it.
Illustration: Fig. 34.—The Biceps Muscle dissected to show its Tendons.
72. Synovial Sheaths and Sacs. The rapid movement of the tendons over
bony surfaces and prominences would soon produce an undue amount of
heat and friction unless some means existed to make the motion as easy
as possible. This is supplied by sheaths which form a double lining
around the tendons. The opposed surfaces are lined with synovial
membrane,[11] the secretion from which oils the sheaths in which the
tendons move.
Little closed sacs, called synovial sacs or bursæ, similarly lined and
containing fluid, are also found in special places between two surfaces
where much motion is required. There are two of these bursæ near the
patella, one superficial, just under the skin; the other deep beneath
the bone (Fig. 29). Without these, the constant motion of the knee-pan
and its tendons in walking would produce undue friction and heat and
consequent inflammation. Similar, though smaller, sacs are found over
the point of the elbow, over the knuckles, the ankle bones, and various
other prominent points. These sacs answer a very important purpose, and
are liable to various forms of inflammation.
Experiment 21. Examine carefully the tendons in the parts dissected in
Experiment 18. Pull on the muscles and the tendons, and note how they
act to move the parts. This may be also admirably shown on the leg of a
fowl or turkey from a kitchen or obtained at the market.
Obtain the hoof of a calf or sheep with one end of the tendon of
Achilles still attached. Dissect it and test its strength.
73. Mechanism of Movement. The active agents of bodily movements, as we
have seen, are the muscles, which by their contraction cause the bones
to move one on the other. All these movements, both of motion and of
locomotion, occur according to certain fixed laws of mechanics. The
bones, to which a great proportion of the muscles in the body are
attached, act as distinct levers. The muscles supply the power for
moving the bones, and the joints act as fulcrums or points of support.
The weight of the limb, the weight to be lifted, or the force to
overcome, is the resistance.
74. Levers in the Body. In mechanics three classes of levers are
described, according to the relative position of the power, the
fulcrum, and the resistance. All the movements of the bones can be
referred to one or another of these three classes.
Levers of the first class are those in which the fulcrum is between the
power and the weight. The crowbar, when used to lift a weight at one
end by the application of power at the other, with a block as a
fulcrum, is a familiar example of this class. There are several
examples of this in the human body. The head supported on the atlas is
one. The joint between the atlas and the skull is the fulcrum, the
weight of the head is the resistance. The power is behind, where the
muscles from the neck are attached to the back of the skull. The object
of this arrangement is to keep the head steady and balanced on the
spinal column, and to move it backward and forward.
Illustration: Fig. 35.—Showing how the Bones of the Arm serve as
Levers.
P, power;
W, weight;
F, fulcrum.
Levers of the second class are those in which the weight is between the
fulcrum and the power. A familiar example is the crowbar when used for
lifting a weight while one end rests on the ground. This class of
levers is not common in the body. Standing on tiptoe is, however, an
example. Here the toes in contact with the ground are the fulcrum, the
power is the action of the muscles of the calf, and between these is
the weight of the body transmitted down the bones of the leg to the
foot.
Levers of the third class are those in which the power is applied at a
point between the fulcrum and weight. A familiar example is where a
workman raises a ladder against a wall. This class of levers is common
in the body. In bending the forearm on the arm, familiarly known as
“trying your muscle,” the power is supplied by the biceps muscle
attached to the radius, the fulcrum is the elbow joint at one end of
the lever, and the resistance is the weight of the forearm at the other
end.
Experiment 22. _To illustrate how the muscles use the bones as levers._
First, practice with a ruler, blackboard pointer, or any other
convenient object, illustrating the different kinds of levers until the
principles are familiar. Next, illustrate these principles on the
person, by making use of convenient muscles. Thus, lift a book on the
toes, by the fingers, on the back of the hand, by the mouth, and in
other ways.
These experiments, showing how the bones serve as levers, may be
multiplied and varied as circumstances may require.
75. The Erect Position. The erect position is peculiar to man. No other
animal naturally assumes it or is able to keep it long. It is the
result of a somewhat complex arrangement of muscles which balance each
other, some pulling backwards and some forwards. Although the whole
skeleton is formed with reference to the erect position, yet this
attitude is slowly learned in infancy.
In the erect position the center of gravity lies in the joint between
the sacrum and the last lumbar vertebra. A line dropped from this point
would fall between the feet, just in front of the ankle joints. We
rarely stand with the feet close together, because that basis of
support is too small for a firm position. Hence, in all efforts
requiring vigorous muscular movements the feet are kept more or less
apart to enlarge the basis of support.
Now, on account of the large number and flexibility of the joints, the
body could not be kept in an upright position without the cooperation
of certain groups of muscles. The muscles of the calf of the leg,
acting on the thigh bone, above the knee, keep the body from falling
forward, while another set in front of the thigh helps hold the leg
straight. These thigh muscles also tend to pull the trunk forward, but
in turn are balanced by the powerful muscles of the lower back, which
help keep the body straight and braced.
The head is kept balanced on the neck partly by the central position of
the joint between the atlas and axis, and partly by means of strong
muscles. Thus, the combined action of these and other muscles serves to
balance the body and keep it erect. A blow on the head, or a sudden
shock to the nervous system, causes the body to fall in a heap, because
the brain has for the time lost its power over the muscles, and they
cease to contract.
Illustration: Fig. 36.—Diagram showing the Action of the Chief Muscles
which keep the Body Erect. (The arrows indicate the direction in which
these muscles act, the feet serving as a fixed basis.) [After Huxley.]
_Muscles which tend to keep the body from falling forward._
A, muscles of the calf;
B, of the back of the thigh;
C, of the spinal column.
_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 passions of the individual. Two important muscles, the temporal,
near the temples, and the masseter, 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 passes 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, Δ. The biceps,
or two-headed muscle, forms a large part of the fleshy mass 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 mass 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 passes 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.”
Illustration: Fig. 37.—A Few of the Important Muscles of the Back.
Passing 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 retard 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 quantity, 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.
Illustration: Fig. 38.—Principal Muscles on the Left Side of Neck.
A, buccinator;
B, masseter;
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
circumstances, 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 retards 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 glass, in a little water. Continue until the
pieces are almost invisible to the naked eye.