shape and direction of the shoulder-blade--the Monkey is intermediate
between Man and the inferior animals. The Monkey’s chest is broad
and round, in proportion to its length, if we compare it with other
animals; but this is less marked than in the human chest. And you
perceive that the Monkey’s back-bones project, as they do in other
animals, beyond the level of the ribs. The blade-bones are also like
those of Man in being prolonged downwards, and in being carried, to a
certain extent, across the ribs; but their lower angles do not run so
far in this direction as they do in the human skeleton.
[Illustration: Fig. 59. Monkey.]
The movement of raising the arm, as in carrying the hand _outwards_,
or pointing upwards, or putting the hand upon the head, is rather a
difficult one, and requires the combined action of many muscles. It
is, therefore, to be avoided by persons to whom muscular straining is
likely to be injurious; and the power of effecting this movement is
easily impaired by accident or disease. A long time often elapses even
after a slight bruise of the shoulder, before the person recovers the
power of putting the hand upon the head.
The exercise of raising the arms above the head is a good one for
those in health, and is much, and wisely, recommended by the directors
of gymnastics. It brings many muscles into play, not only those of
the shoulder, but the muscles all round about the chest, viz. those
which pass from the spine and ribs, as well as from the breast-bone,
head, and pelvis, to the shoulder-blade and arm; and, thus, it tends
to strengthen the spine and the chest, as well as the shoulders and
arms. There is, perhaps, no exercise so good as this; and it is much
to be regretted that the dress of young ladies, with its paraphernalia
of stays and shoulder-straps, interferes so greatly with it. The
frequency among them of “pigeon-breast” and “crooked spine” must,
partly, be attributed to the confinement of the arms, caused by the
mode of dress and the customs of life. One of the few opportunities
afforded to the arms of availing themselves of this exercise is in the
dressing-room during the process of brushing the hair. I would by all
means, therefore, recommend young ladies to give sufficient time and
attention to this part of the toilette, and not to delegate it to the
lady’s maid. If, in addition, I suggest that it be commonly done with
open window, I feel sure that I shall have a deservedly great authority
among them--Miss Nightingale--on my side.
[Illustration: Fig. 60. Elbow-joint.]
The movement at the ELBOW is, merely, that of bending and
straightening, in a hinge-like manner; yet there is a slight obliquity
in the direction in which it takes place, an obliquity resembling that
in the movement at the knee (page 39).
_Pronation and Supination of the Hand._
In the FOREARM and HAND there is a movement with which we have
nothing exactly corresponding in the leg. It is called “Pronation
and Supination.” In _pronation_ we turn the palm _down_wards, as in
picking up any substance from a table; in _supination_ we turn the palm
_up_wards, as a boy does when he holds out his hand for a caning, or
for the more agreeable purpose of having a shilling put into it.
PRONATION and SUPINATION take place in the following manner. Each of
the two bones of the forearm extends from the elbow to the wrist (fig.
53); but one of them--the “ulna”--is chiefly connected with the elbow;
and the other--the “radius”--is chiefly connected with the wrist, and,
by means of the wrist, with the hand. The two bones are separate from
one another, except at their ends. There they touch, and are jointed
together in such a manner that the large lower end of the radius can
play round, or partly round, the small, button-like, lower end of the
ulna; and, in so doing, it carries the hand with it. In this movement
the upper end of the radius (A, fig. 60) does not leave its place,
but simply revolves, upon its own axis, on the surface of the arm-bone;
and its edge turns in a notch cut for it in the upper end of the ulna
(B), which remains still.
[Illustration: Fig. 61.
Hand supine.]
[Illustration: Fig. 62.
Hand prone.]
In the drawings (figs. 61 and 62) the relation of the parts in
the supine and in the prone state is shown by the aid of a plumb-line
falling from the part of the arm-bone upon which the upper end of
the radius revolves. The line traverses the upper end of the radius,
then passes along the interval between the two bones, then traverses
the lower end of the ulna, and, finally, takes the course of the ring
finger. And, provided the limb be held vertically, the line traverses
the same parts whatever be the position of the forearm and hand. It
does so in complete supination, as shown in fig. 61; it does so
in complete pronation, as shown in fig. 62; and it does so in
every intermediate position. We may call it, therefore, the axis upon
which the radius and the hand turn in pronation and supination; and,
according to this representation, the ring finger remains stationary
during the movement, while the other fingers and the thumb perform
their partial revolutions around it.
I have said there is no movement in the lower limb exactly like the
pronation and supination of the forearm and hand. We have, it is true,
a power of moving the leg upon the thigh in a somewhat similar manner;
but this can only be done when the knee is bent. For instance, when
sitting in a chair with the foot upon a fender, or with the toes upon
the ground, we can make the foot revolve so as to turn the heel in
or out. A little careful observation, however, will prove that this
movement takes place, altogether, at the knee, and that _both_ bones
of the leg participate equally in it, the _whole_ leg revolving with
the foot. Whereas, in the case of the forearm, the movement takes
place, partly, at the wrist, and, partly, at the elbow; and _one_ bone
(the ulna) remains _still_ while the lower end of the other bone (the
radius) revolves around it. Moreover, the pronation and supination of
the hand and forearm are much more free than these movements of the
foot and leg; and they take place with equal facility and freedom in
any position of the limb. We can turn the palm up or down as easily
when the elbow is straight as when it is bent.
The movement of which I am speaking is so important to the usefulness
of the hand, that I will call your attention to three of the muscles by
which it is effected.
And, let me remark, by the way, that all the movements in the solid
parts of the body--probably all without exception, even the slight
wrinklings of the skin that take place when it is exposed to cold--are
the result of muscular action. Muscles are bundles of fibres which
have usually a red colour and constitute what is commonly called the
“flesh” or “lean meat” of animals. They are endued with the power
of contracting or shortening themselves; and it is this property
which gives rise to the various movements of animal bodies. At their
ends muscles often dwindle into “tendons” or “sinews” which, though
occupying much less space, and having no contractile power, are very
strong, and serve to connect the muscles with the bones.
One of the three muscles just mentioned (A, fig. 61) passes from
a projecting process on the inner side of the arm-bone, at its lower
end, to the outer edge of the middle of the radius. Its contraction
causes the radius to roll over, or in front of, the ulna. It thus
pronates the hand, and is called a “_Pronator_” muscle. Another muscle
(B, fig. 62) passes, from a projecting process on the outer side
of the arm-bone, to the inner edge of the radius near its upper part.
It runs, therefore, in an opposite direction to the former muscle and
produces an opposite effect, rolling the radius and the hand back into
the position of supination. Hence it is called a “_Supinator_” muscle.
[Illustration: Fig. 63. The Biceps Muscle.]
The third is a very powerful muscle. It is called the “_Biceps_”
muscle (fig. 63), because it has _two_ points of attachment to the
shoulder-blade. It descends along the front of the arm, and, bulging
there, forms a conspicuous feature, to which athletic persons are proud
to point in evidence of their muscular development. Its tendon crosses
over the front of the elbow, and is inserted into the hinder edge of a
stout tubercle which is seen on the inner side of the radius near its
upper end. The chief effect of this muscle is to bend the elbow; but it
also rotates the radius so as to supinate the hand; and it gives great
power to that movement. When we turn a screw, or drive a gimlet, or
draw a cork, we always employ the _supinating_ movement of the hand for
the purpose; and all screws, gimlets, and implements of the like kind,
are made to turn in a manner suited to that movement of the right hand,
because mechanicians have observed that we have more power to supinate
the hand than to pronate it, though they are, probably, not aware that
the preponderating influence of the _biceps_ muscle is the cause of the
difference.
The movement of which I am speaking is performed to its full extent
only by Man. Monkeys cannot completely supinate the hand; and in most
of the lower animals the part corresponding with the hand remains
nearly, or quite, fixed in a state of pronation. Even in Man, complete
supination is rather a constrained and awkward position. It is not
a position which is habitual or natural to us. When we see any one
sitting or walking with the palms turned forward it strikes us as
strange, and the idea is suggested to us that the individual must be
strange too, that, possibly, his head may be a little turned as well as
his hands. In a state of ease the hand is naturally more or less prone;
so that when it is desired to place the forearm or hand at rest, as
in case of disease or injury, the prone position is usually selected.
If the forearm be broken, for instance, the surgeon sets the fracture
and fixes the limb with the hand prone or semiprone. This is, also,
the position of greatest strength, as well as of most ease. Hence, in
striking a blow, or carrying a weight, or making any strong muscular
effort, the palm is always kept more or less inturned.
_The Wrist._
[Illustration: Fig. 64. Wrist-joints.]
This drawing (fig. 64) represents what is seen when a section has
been made, from side to side, through the wrist and lower part of the
forearm. It gives an idea of the mode in which the several bones of the
wrist are adapted to one another and held together by ligaments. The
upper three wrist-bones (C, E, D) are joined together, so as to present
a convex surface, which is received into a wide cup, or socket, formed
by the end of the radius (A) and a ligament passing from the radius to
the ulna (B); and, in pronation and supination, the end of the radius,
together with this ligament and the wrist-bones, revolves upon the end
of the ulna.
All the bones here represented are so well fitted to one another, and
so strongly bound together, that, as I have before said, displacement
very rarely occurs among them. We sometimes _hear_ of a dislocation of
the wrist, but very seldom _see_ one. The wrist is often bruised, or
its ligaments strained, by falls upon the hand; or, what very often
happens, especially after the middle period of life, the bones of the
forearm are broken a little above the wrist.
You might think that, in such an accident, the radius only would
suffer, inasmuch as it is especially connected with the wrist-bones,
and so receives the force directly from the hand. But, if you observe
the line of contact of the radius and ulna (running from F), you will
see that it is oblique, and that its direction is such as to cause the
ulna to support the radius, and to receive some of the force from it;
and this disposition, which makes the ulna share the duties of the
radius, makes it, also, share the dangers; hence, it is very frequently
involved with the radius in fracture of the forearm.
By the joints of the wrist we are enabled to move the hand backwards
and forwards, and also slightly sideways.
_The Movements of the Hand._
I come now to speak more particularly of the movements that take
place in the Hand. I have already said that the mobility of the thumb
is the chief characteristic of the hand as distinguished from the
foot. Another important distinction between the hand and the foot is
the greater length and mobility of the fingers as compared with the
toes. The toes are short; and our power of moving them is, under any
circumstances, slight. They constitute a small, and, comparatively,
unimportant, part of the foot. The fingers, on the contrary, are long;
they form a half, and, including the thumb, the more important half,
of the hand. Without them the rest of the hand, indeed the rest of the
limb, would be comparatively useless. Their movements are varied and
free, and take place with singular facility and rapidity. We can bend
them quite down upon the palm, and can extend them beyond the straight
line; we can separate them from one another to a considerable extent;
and we can bring them together with some force, as a waiter does when
he carries a number of wine-glasses between his fingers; and persons
who have lost the thumb contrive to hold a pen, a knife or fork, or
other things, between the fingers.
[Illustration: Fig. 65.
Muscles of forearm and hand.]
Let me endeavour to give you an idea of some of the muscles which are
concerned in executing these movements.
The wrist and hand are bent forwards upon the forearm by means of
three muscles (A, B, C, fig. 65). These all pass downwards from
the inner side of the lower end of the armbone. The outer and inner
ones (A and C) are connected, by tendons, with the wrist-bones; and the
tendon of the middle one (B) runs over the wrist and becomes spread
out in the palm like a fan, so as to support the skin of the palm and
to protect the nerves and blood-vessels, which lie beneath it, from
injurious pressure, when we grasp any substance firmly in the hand. The
fan-like expansion of this tendon in the palm is called the “palmar
fascia.” It is very strong, and is connected, below, with the ends of
the metacarpal bones, and with the sheaths of the fingers. The bundle
of muscles near D forms what is called the “ball of the thumb,” and
serves to move the thumb in various directions.
[Illustration: Fig. 66.
Muscles and tendons of hand.]
Beneath these three muscles which bend the wrist and strengthen the
palm lies another set of muscles (A, B, fig. 66) which bend the
thumb and fingers. They pass from the bones of the forearm, and end in
long tendons or “leaders” which run over the wrist and palm and along
the fingers and are firmly connected with the last phalanges of the
fingers. They lie close to the bones in their whole course, and are
held in their places by sinewy cross bands and sheaths which are seen,
both at the wrist and in the fingers, in fig. 65.
[Illustration: Fig. 67.
Muscles and tendons on back of forearm and hand.]
Fig. 67 represents the muscles on the back of the forearm. The
tendons pass from them, and run, some to the wrist and extend, or bend
backwards, the wrist upon the forearm, some to the thumb and extend the
several joints ofthe thumb; and others run to the back of the fingers. These leaders
lie nearer to the skin than do those on the palmar aspect; and most of
those which go to the thumb and fingers may be distinguished through
the skin. The short muscles (A, A) situated upon and between the
metacarpal bones pass from them to the sides of the fingers; some of
these serve to spread the fingers out from one another, while others
have the effect of drawing them together. There are several such small
muscles on both surfaces of the hand, but I must not detain you by
a description of them; and there are other little muscles passing
from the flexor tendons to the phalanges, which have been called
_fidicinales_, from their assisting in performing the short quick
motions of the fingers, and from their being, accordingly, called into
action in playing upon the violin and other musical instruments.
_Movements of the Thumb._
In its adaptation to the purposes of bearing the weight and
ministering to the locomotion of the body the human foot excels that
of any other animal; and, unquestionably, the human hand is not less
preeminently distinguished by the nicety, the variety, and the freedom
of its movements. This is shown by the manner in which it can be
twisted about, by the exquisite play of the fingers; and it is shown,
above all, by the mode in which the thumb can be moved to and fro, can
be opposed to the other fingers, and to any part of them individually
and collectively, and can be folded beneath them or clasped upon them
as occasion may require.
The power which the thumb possesses, and gives to the hand, is
signified by its name--“pollex,”--derived from the Latin word
_pollere_, which means to have power. Some have supposed that the word
“poltroon” is derived from _pollice truncato_, and signifies one so
cowardly that he has submitted to have his thumb cut off in order that
he may be incapacitated for fighting.
The faculty which we possess of moving the thumb in the way I have
mentioned, athwart the other fingers, and of touching any part of the
palmar surface of either of them depends, partly, upon its being set,
not quite in the same plane with them, but, obliquely, so that when it
is moved towards the palm it faces or opposes the other fingers; and,
partly, upon the nature of the joint between its metacarpal bone and
the bone of the wrist with which it is connected.
This joint is so constructed as to admit of three different movements.
_First_, the thumb can be moved forwards or backwards, that is,
towards, or, away from, the palm. _Secondly_, it can be “adducted” or
“abducted,” that is, approximated to the forefinger or inclined away
from it. _Thirdly_, it can be “circumducted,” that is, its extremity
can be made to describe a circle, as in “twiddling the thumbs.” These
several movements are effected with great power and rapidity by
means of the bundle of muscles which forms the “ball of the thumb”
(fig. 65. D), as well as by the long muscles and tendons which
descend, from the forearm, to the thumb.
_Movements of the metacarpal bones of the Fingers upon the Wrist._
The movements of the thumb, through the medium of its metacarpal bone,
upon the wrist are much more free than those of any of the other
fingers. The middle finger, indeed, has its metacarpal bone set upon
the wrist so fixedly as to admit of scarcely any such movement. The
forefinger can be thus moved a little; the ring finger more and the
little finger still more.
You may easily prove this by taking the knuckles or heads of the
respective metacarpal bones of one hand between the fingers and thumb
of the other hand, when you will find that you can press the knuckle of
the little finger backwards and forwards in a very perceptible manner.
Then try the knuckle of the ring finger; the movement is distinct,
though not so free as in the case of the little finger. The knuckle of
the forefinger you will find to be almost fixed; and in that of the
middle finger you will be unable to perceive any movement at all.
In fact the joints of the metacarpal bones of the fingers with the
wrist resemble those of the outer four toes with the tarsus; and the
drawings of these joints of the foot (figs. 22 to 25) will serve
sufficiently well to illustrate those of the hand.
These movements of the metacarpal, or knuckle, bones upon the wrist
enable us to increase or diminish the hollow of the palm by bringing
its edges more or less forward. Thus, when we make a cup of the hand we
bring forward the metacarpal bones of the thumb and the little finger,
wrinkling the skin of the palm; and when we spread the hand open we
carry those bones backwards, rendering the skin of the palm tense.
These movements, moreover, enable us to bring the little fingers and
the thumb more easily into contact.
Have you ever wondered what advantage is gained by the fingers and
thumb all differing from one another in length; or don’t you take the
trouble to reflect upon little matters of this sort? If you have, I
would ask you now to remark that there is, in the several fingers,
a relation between their shortness, their position near the edge of
the hand, and the amount of mobility of their metacarpal bones upon
the wrist. Thus the finger which is in the middle of the hand is
the longest, and its metacarpal is the most fixed. The fore-finger
is not quite so long; and its metacarpal is rather less immovable.
The ring-finger comes next in shortness and in the mobility of its
metacarpal. Then the little finger; and the thumb which is much shorter
than any other has also its metacarpal much more moveable.
[Illustration: Fig. 68.]
Observe, further, that, when the fingers and thumb are separated from
one another, and then bent, the middle knuckle-bone remains stationary,
but the others are advanced a little forwards, each to an extent
proportionate to its mobility upon the wrist, and to the shortness of
the finger. The fore-finger is, by this means, advanced a little, the
ring and the little fingers more, and the thumb most of all. And the
result is, that the tips of the fingers and the thumb come all to a
level, and form, with the palm, a great hollow in which we can grasp
any substance, a cricket-ball, for instance, and hold it very firmly.
The length of the several fingers and the thumb is, therefore, just so
regulated, in relation to their mobility upon the wrist, as to give us
this power.
You may observe, also, that when the fingers and the thumb are spread
out the space between the thumb and the fore-finger is considerably
greater than either of the spaces between the other fingers. Then, by a
slight movement, the thumb takes up a position in front of, or opposite
to, the fingers; and in grasping any substance it has to antagonise the
pressure exerted by all the fingers. Hence it needs to be much stronger
than they are, and to be wielded by more numerous and more powerful
muscles.
The MIDDLE FINGER is not only the longest and the largest finger; it
is also, to a certain extent, the centre about which the others move.
Thus, when the fingers are bent down into the palm, their tips all
converge towards the middle finger; and when they are spread out, they
all diverge from it. Its greater length and the greater prominence
of its knuckle, expose this finger to injury more than any of the
others; which may account for the fact that Surgeons are called upon
to amputate the middle finger more frequently than either of the other
fingers or the thumb.
The FORE-FINGER has the greatest range of independent movement. Hence
it is used to point with, and is called the “Index” or “Indicator”
finger.
_Writing._
In WRITING the pen should be held between the pulps of the fore and
middle fingers and the thumb, in contact with all three, and firmly
lodged between them. The down-stroke is made by bending the phalanges
of the fingers and the thumb inwards and the metacarpal bone of the
thumb outwards; and the up-stroke is made by straightening all the
joints of the fingers and thumb. The hand rests lightly, not upon its
whole edge, but, upon the hindermost and foremost parts of the edge,
that is, upon the pisiform bone of the wrist and upon the little finger
near the end, so that it can be moved easily along the paper, and can
be inclined, or rolled, a little to either side. The obliquity of the
stroke is not imposed by mere arbitrary rule, but is in accordance with
the direction in which there is the freest movement of the fingers and
thumb when thus holding the pen. Make the experiment for yourselves of
moving the pen in different directions, and you will soon be satisfied
that the writing-master has nature on his side in insisting on a
particular movement as well as a particular mode of holding the pen.
Some persons make the strokes vertical, or slope them the wrong way;
but in either case the writing is stiff and awkward; it is not natural.