The part peculiar to a muscle is what is commonly called the muscular
fibre; the vessels, the nerves, the exhalants, the absorbents and the
cellular texture, which is very abundant around this fibre, form its
common parts.
I. _Texture peculiar to the Organization of the Muscular System of
Animal Life._
The muscular fibre is red, soft, of an uniform size in the great
and small muscles, sometimes disposed in very evident fasciculi and
separated from each other by remarkable grooves, as in the gluteus
maximus, the deltoid, &c. sometimes more equally in juxta-position, as
in most of the broad muscles, always united to many others of the same
nature like it, easily by this union distinguished by the naked eye,
but eluding microscopic researches when we wish to examine it in a
separate manner, so great is its tenuity. Notwithstanding this extreme
tenuity, an infinite number of researches have been made during the
last age, to determine with precision the size of this fibre. On this
point may be read the result of the labours of Leuwenhoek, Muysk, &c. I
shall not give here this result, because science can draw nothing from
it, and because we cannot rely upon its accuracy; of what importance
moreover is the precise size of the muscular fibre? its knowledge would
add nothing to our physiological views upon the motion of the muscles.
Every muscular fibre runs its course without bifurcating or dividing
in any manner, though many have thought otherwise; it is found only
in juxta-position to those which are near it, and not intermixed, as
often happens in the fibrous system; an arrangement that was rendered
necessary by the insulated motions it performs; for the general
contraction of a muscle is the union of many partial contractions,
wholly distinct and independent of each other.
The length of the fleshy fibres varies very much. If we examine in
general the mass which they form by their union, we observe that this
mass has sometimes much greater extent than the tendinous portion of
the muscle, as the biceps, the coraco-brachialis, the rectus internus
femoris, &c.; that sometimes its length is much less as in the small
plantar and palmar muscles, &c.; and that sometimes it is about equal,
as in the external radial, &c. If from the examination of the fleshy
mass, we pass to that of the separate fibres that compose it, we
see that the length of the first is rarely the same as that of the
second. There are hardly any but the sartorius and some analogous
muscles, whose fibres run the whole extent of the fleshy, mass; in
almost all the others, they are found obliquely arranged between two
aponeuroses, or between a tendon and an aponeurosis; so that though
each of them may be very short, as a whole they are very long, as we
observe in the anterior rectus of the thigh, the semi-membranosus, &c.
This arrangement may also arise from various tendinous intersections,
which cut at different distances the length of the fibres. In general,
the muscles which owe their length to long fibres, have great extent
and very little power of motion; whilst those with short fibres, but
multiplied so as to give great length as a whole, are remarkable for
an opposite character. And this is the reason: all the fibres being
equally large, whatever may be their length, have the same degree of
force; it is evident then that this force considered in a muscle as
a whole, is measured by the number of its fibres. On the other hand,
the longer a fibre is, the more it shortens in its contraction; then
by contracting, a muscle brings its attachments so much the nearer in
proportion as its fibres are longer.
All the fibres of the voluntary muscles are straight, those of the
sphincters excepted. They are either parallel as in the rhomboids, or
obliquely situated in relation to each other, as in the great pectoral.
Sometimes in the same muscle many sets cross each other in different
directions, as we see in the masseter; but this crossing is wholly
different from that of the involuntary muscles in which there is more
crossing of fibres, whilst here we see only fasciculi in different
directions, in juxta-position to each other.
I shall not speak here of the cylindrical form according to some, and
the globular one according to others, of the fleshy fibre; inspection
teaches us nothing upon this point; how then can we make that an object
of research and give an opinion upon it, which has no real foundation?
Let us say thus much of the intimate nature of this fibre, upon which
so much has been written. It is unknown to us, and all that has been
said upon its continuity with the vascular and nervous extremities,
upon its pretended cavity, upon the marrow, which according to some
filled it, &c. is only a collection of vague ideas, which nothing
positive confirms, and to which a methodical mind would not attend. Let
us begin to study nature where she begins to come under our senses. I
would compare the anatomical researches upon the intimate structure
of the organs, to the physiological researches upon the first causes
of the functions. In both we are without guides, without precise and
accurate data; why then give ourselves up to them?
All that we can know upon the nature of the muscular fibre, is that it
is peculiar, that it is not the same as that of the nerves, nor as that
of the vessels, nor as that of the tendons or the cellular texture; for
where there is identity of nature, there ought to be identity of vital
properties and of texture. Now we shall see that all these systems
differ essentially from each other in this point of view; there can
be between them no analogy in relation to their nature, whence the
properties are always derived.
The muscular texture is remarkable for its softness and small degree
of resistance. It is by this that it is essentially different from the
fibrous texture. It breaks with ease in the dead body. In the living,
this rupture is rare, because the contraction which exists in all the
violent efforts, gives it a density, by which it gains an enormous
increase of resistance, but which it loses when it is no longer in
a state of contraction. There are however examples of the rupture
of muscles; it is principally in the rectus abdominis and quadratus
lumborum that they take place. I have seen one in this last. Observe
that this muscle and all those placed between the ribs and the pelvis,
are much disposed, from their situation, to these ruptures. In fact,
when the pelvis and the thorax are carried in an opposite direction,
these muscles are so much the more violently stretched, as in these
motions all the superior part of the body forms with the thorax, a
great lever, which is moved in an opposite direction to another great
lever, which is formed by the pelvis and all the inferior parts; now
from their length, these levers are capable of receiving a very great
motion, of communicating it consequently to the abdominal muscles which
are stretched between the two, and which serve to unite them. Hence how
in a violent inclination to the right, the quadratus of the left side
can be torn, &c. Observe that but few of the muscles in the economy are
found between two levers so great, consequently are capable of being
so much distended, and especially of being so with a force greater
than that of their contraction; for every muscular rupture supposes
the excess of the external motion, which distends, over that of the
fleshy fibres which contract to oppose this distension. If the external
efforts were concentrated upon a single muscle, they would be able more
often to overcome the resistance; but almost always many partake of the
effort to support and the resistance to oppose.
_Composition of the Muscular Texture._
The muscular texture has been with chemists, a more particular object
of research than most of the other organized textures. They have
examined it under all its relations. I refer to their works, to that
of Fourcroy especially, for all which is not strictly relative to
the nature of this texture, for all which considers consequences not
applicable to physiology, which we can deduce from the knowledge of the
principles that enter into its composition.
Exposed to the action of the air, the muscular texture is affected in
two ways. 1st. It dries, if cut into thin slices, admitting of the
evaporation of the fluids it contains. Then its appearance is of a dull
brown; its fibres contract, it becomes thinner, hard and brittle. If
replunged into water within some days, even fifteen or thirty after its
drying, it resumes its primitive softness and form, and has a less deep
coloured tinge. The water that has been used for this softening is more
or less fetid, and similar to that of macerations. 2d. Exposed in too
great a mass to the air, the muscular texture does not dry, but becomes
putrid. Thus in making anatomical preparations by drying, care should
be taken to lessen the thickness of the fleshy parts, or to arrange
them so that the air can penetrate them everywhere. Putrefaction is
inevitable if the air is moist, if the evaporation of the fluids is
not quick enough to produce drying. When it becomes putrid, the muscle
assumes a green, livid colour; it exhales an offensive odour. Under the
influence of the same circumstances it becomes putrid much quicker than
the fibrous, the cartilaginous and the fibro-cartilaginous systems. The
odour that it exhales then is also very different from that of these
systems; a phosphoric light often escapes from it. A mass of putridity,
in which all the fibres have almost disappeared, takes the place of the
muscle, when putrefaction is advanced. This mass of putridity gradually
evaporates in part, and there remains a dark brown residue, which dries
and becomes hard and brittle, nearly like the muscle dried in the
ordinary state, though the appearance however may be very different.
Exposed to the action of water, the muscle undergoes different
phenomena, according as it is hot or cold. Cold water takes from it at
first its red colour, of which it appears to dissolve the principle. To
effect quickly this phenomenon, it is necessary to expose the flesh,
at first in thin layers, to the action of water that is often changed,
by placing a muscle for example under a fountain, in the current of a
river, or what is much better, by frequently expressing the water it
imbibes; for if we keep it in a vessel, its exterior only whitens a
little, and the interior preserves its colour. Water which has been
used to wash a muscle, looks like blood spread out in this fluid; it
contains the colouring matter, a little of the extractive substance,
gelatine, &c. I believe that of all the organs the muscle is that from
which we remove most easily its colour by artificial means. Ought we
to be astonished after this, if nature varies so evidently and so
frequently this colour by the phenomena of nutrition, as we soon shall
have occasion to remark? Kept in water at a moderate temperature,
the muscular texture remains for a long time without softening; it
finally does, and changes layer by layer into a kind of putridity
very different however from that which is formed in the open air, as
I have frequently observed in macerating the muscles in a cellar, the
temperature of which is uniform. At other times, instead of putrefying
thus, the muscle is changed, as Fourcroy has remarked, into a substance
like spermaceti; then its fibre is hard and solid. But all the muscles
when kept in water by no means exhibit this phenomenon. When it does
take place, very often a kind of reddish product, scattered here and
there on the surface of the muscle, and which is an evident effect of
decomposition, announces and afterwards accompanies this state, without
which also, it often takes place. Maceration in dissecting rooms
frequently exhibits this phenomenon.
When we have taken from the muscles their colouring substance by
repeated washings, there remains a white fibrous texture, from which
we can still extract albumen by ebullition, which rises in scum,
gelatine by suffering it to grow cold, extractive matter which has a
deep colour, by letting it settle, and some phosphoric salts. When
all these substances have disappeared, the residue of the muscle is
a fibrous substance, of a greyish colour, insoluble in warm water,
soluble in the weak acids, giving out much azote from the action of the
nitric acid, and presenting all the characters of the fibrin of the
blood. It appears, as Fourcroy has remarked, that this substance is
truly the nutritive substance of the muscle, that which, continually
exhaled and absorbed, contributes to its nutritive phenomena more
than all the others; it constitutes the essence of the muscle, it
especially characterizes it, as the phosphate of lime is the nutritive
characteristic matter of the bones. Is this substance formed in the
blood and carried from it to the muscle, or is it formed in the muscle
by nutrition, and thence carried to the blood? I know not. Whichever
may be the case, it appears to experience very great varieties in
its exhalation and absorption. The state of laxity, of cohesion, the
thousand various appearances of the muscular texture, appear to belong
in part to these varieties of proportion. Thus the phosphate of lime
or gelatine, diminished by nutrition, give to the bones softness or
brittleness.
It is in this fibrous and essential portion of the muscle, that
particularly resides the faculty of crisping by the action of caloric,
whether by plunging a muscle into boiling water, or exposing it to the
fire; for this crisping is as evident in the muscle deprived of its
colouring matter, its gelatine, its albumen, and even a portion of its
extractive substance as in the ordinary muscle. There is in general
a constant relation between the quantity of this fibrous substance
contained in the muscles, and the quantity that the blood contains of
it. In the strong, vigorous, sanguineous temperaments, as they are
called, the muscles are thick and much more fibrous. In all the slow
cachexiæ in which the blood is impoverished, the pulse small and feeble
and in which muscular nutrition has had time to share but little of the
fibrin of the blood, the muscles are small, weak, soft, &c. In general,
the muscles and the blood are always in constant relation, whilst other
systems often predominate and whilst this fluid seems to be in less
quantity in the economy.
Exposed for a long time to ebullition, as in common boiled meat, the
muscular texture, still united to the adjacent organs, and to its
common parts, gives, 1st, an albuminous scum which appears to arise
more from the lymph of the cells than from the muscle itself; 2d,
many fatty drops coming also especially from the cellular texture,
almost foreign consequently to the texture of the muscle, and which
swim on its surface; 3d, gelatine formed especially by the aponeurotic
intersections; 4th, an extractive substance which colours in part the
water in which it is boiled, gives it a peculiar taste and remains in
part adherent to the flesh to which it communicates a deep tinge wholly
different from that of raw flesh, a tinge which arises also from the
colouring matter of the muscle, and which moreover changes, when the
liquor cools, into a less deep and even a whitish tinge; 5th, various
salts which contribute much to the taste of the liquor, and the nature
of which chemists have ascertained. These are the natural phenomena of
the ebullition of the muscle.
The more extensive analysis of boiled flesh is not my province; but
what ought not to escape us here, are the phenomena of which the
fibre is the seat, whilst the preceding products are extracted,
whether from it, or the surrounding textures. These phenomena can
be referred to three periods. 1st. When the water is only tepid,
and even a little above the temperature of the body, it leaves the
muscular texture in the same state, or softens it a little. 2d. When
it approaches ebullition and begins to be covered with an albuminous
scum, the texture crisps, thickens and contracts and gives to the
muscle a density much greater than what is natural to it, and
augments considerably its resistance. I have observed that in this
state the muscles bear much greater weights than in a natural state.
They approximate, if we may so say, that remarkable density which
characterizes them when they contract in the living body, and which so
powerfully opposes their rupture. This condensation of the muscular
texture, which is prompt and sudden, increases till the period of
ebullition, when it is at its greatest height; it continues only for
a certain time. 3d. Gradually it diminishes, the fibres soften, and
are more easily torn than in their natural state. This softening, the
reverse of the hardening that precedes, is produced slowly and by
degrees. When arrived to a certain degree, the meat is rendered fit
for the table. Observe that then the muscle has not returned to the
state in which it was found before the hardening; among other phenomena
which distinguish it, the following is an essential one; it has lost
the power of crisping, of acquiring the horny hardness, from the action
of the concentrated acids, from alkohol or from caloric. In general it
becomes putrid more slowly. Its putrefaction does not give the same
odour. We know how much its taste differs. The principles it has lost
are undoubtedly one of the great causes of these differences.
When a muscle is exposed to an open fire, as in the roasting of meat,
the albumen is condensed, the gelatine melts, the fibrin filled with
juices softens, the extractive matter flows in part with the gelatine
and the salts held in solution; it is this that forms the gravy,
which is, as we know, very different from melted fat. The exterior of
the meat remains more dense than the interior; it is coloured by the
extractive substance. The interior loses in part its natural colour;
its consistence, its taste and its composition even change entirely.
The fibres, as in ebullition, lose the power of contracting and of
crisping from the action of strong stimuli and especially that of fire.
No part in the animal economy is more easily altered by the digestive
juices than the muscles. Almost all stomachs can bear boiled meat,
whilst many reject other organs when cooked. Carnivorous animals seize
upon the muscles of their prey in preference to the pectoral and
gastric viscera. Muscular flesh is with most people the most common
aliment, that with which they are never disgusted; it appears to be
the most nourishing of all those, which are afforded by the different
textures of animals; is it, as it has been said, because it contains
the most azote? Whatever may be the reason, the general part which the
muscular system takes in the digestion of all carnivorous animals, of
man especially, is remarkable. Yet all the parts of this system do
not appear to be equally agreeable to the taste of animals. It is,
for example, a singular fact, that those bodies which are brought to
our dissecting rooms, and which have been attacked by rats, are found
almost always exclusively gnawed in the muscles of the face.
Observe in regard to the use of the muscles in digestion, that it
is the portion of the fibrous system which adheres to them, and
forms, as it were, a part of them, I refer to the tendons, which
is the most easily altered by maceration, by ebullition and by the
digestive juices. Observe also that the great mass which the muscles
form in the body of all animals, of which they are more than one
third, presents to the carnivorous species ample materials for their
nutrition; thus nature, by multiplying these organs for the wants of
the individual which they move, seems to multiply them also for those
of the individuals which he is one day to nourish. In forming them in
each species, it labours for other species as well as for this. Who
knows if this general design, which observation finds in the series of
all animals, be not the cause of this remarkable predominance which
the muscles have over the other systems? Who knows, if nature would
not have diminished the powers of the animal mechanism which are so
numerous and so complicated in comparison with those of artificial
machines, who knows if she would not have simplified the means and
given the same results, if the motions of the animals had been the only
object of the formation of the muscles?
The sex has great influence on the quality of the flesh of animals. I
do not believe that any thing precise is known as to the nature of the
influence which the genital parts exert upon it; but the following are
remarkable facts upon this subject. The muscles of males are stronger
and better nourished, have more taste, resist boiling for a longer
time, are firmer, &c. Boiling water on the contrary alters quicker the
texture of females; it is more tender and gives to the liquor a less
strong taste. In the season of sexual intercourse, the muscular system
of the first has a peculiar odour, which often renders it disagreeable
even to the taste. It is an observation that is easily made in
quadrupeds, birds and fishes that are brought to our tables. Without
having as strong an odour, the flesh of the second becomes at this
period soft, flaccid and but little savoury.
II. _Parts common to the Organization of the Muscular System of Animal
Life._
_Cellular Texture._
The cellular texture is very abundant in the muscular system; I know
of no system that has a greater proportion of it. This texture forms
a very evident covering around each muscle. This covering is most
commonly loose, filled with fat, easily distended with air in emphysema
and serum in anasarca. At other times it is more dense, compact and
really arranged like a membrane. Such, for example, is the case with
that which covers the great oblique muscle of the abdomen, and the
dissection of which on this account, students at first find very
difficult. The other abdominal muscles, the trapezius, the serratus
major and the great dorsal exhibit also this arrangement. We might say
that in this way nature compensated for the aponeuroses, which are
wanting on the broad muscles of the trunk. Besides, this covering has
only a membranous appearance; it has nothing of its organization, it
disappears in the infiltration in which all the true membranes remain.
Besides this general covering of the muscle, each fasciculus has a less
covering, each fibre a still less one, and each smaller one a real
though almost insensible sheath. We can then represent the cellular
texture of the muscles as forming a series of coverings successively
decreasing. These coverings favour the motion of the fibres which they
separate, either by the serum of the cells, or by the fat they contain,
both fluids, by lubricating, allow them to slip more easily upon each
other. Frequently between these fibres, the cellular texture appears
to form a kind of cross pieces which go at right angles. We see this
arrangement especially in the proper extensor of the great toe, and
in the common extensor, the fleshy fasciculi of which are broad and
delicate when distended. In most of the thick muscles nothing similar
is observed.
The quantity of intermuscular cellular texture is remarkably variable.
In general, in all the broad muscles and in all the large, long
muscles, it is very abundant. It is less in proportion between the
fibres of those of the vertebral canals. Back of the neck, the splenii,
complexi, &c. have less of it than many others, especially in the
spaces that separate them.
Sometimes very considerable cellular elongations are found in the
middle of the muscles, and seem to divide them into two; such is that
which separates the clavicular portion of the great pectoral; this
has even sometimes embarrassed anatomists as to the division of these
organs.
The cellular texture in general fixes the muscles in their position;
the art of dissection proves it. The effusions of pus which often
perform the office of the scalpel, render also very evident this use,
which does not prevent the motion in all directions, that the great
extensibility of the cellular texture allows. The cellular texture
not only fixes the muscles to each other, but it also attaches each of
their fibres to neighbouring ones; it flattens them when they contract,
and elongates them when they are distended; if they are deprived of
it their motions become irregular and uncertain. I have many times
separated with a scalpel a muscle laid bare in a living animal, into
many small fasciculi; in afterwards making this muscle contract by
the irritation of the medulla, by means of a stilet introduced into
its canal, I have observed in an evident manner this irregularity of
motion. Cut longitudinally a muscle of an extremity from its superior
tendon to its inferior, so as to divide it into two or three entirely
distinct portions, irritate afterwards one of these portions, the
other or the two others will remain almost always at rest, whilst a
single irritated fibre in a sound muscle, puts in motion the whole of
that muscle. The section of the vessels and the nerves has no doubt a
little influence upon this phenomenon; but that of the cellular texture
certainly contributes to it also.
In dropsical subjects, the serum of the intermuscular texture is often
reddish; this phenomenon is owing to the action of this serum after
death upon the colouring substance. I believe that this can take place
during life only with great difficulty. The fat sometimes abounds in
this texture, to such a degree that the fleshy fibres disappear and
the fat only is visible; but oftentimes also the yellow appearance of
the muscular fibres, which is produced by the absence of the colouring
substance, is taken for this fatty state of the muscles. I have seen
the first state but rarely; the second is extremely frequent; we are
sometimes deceived at first view. But ebullition and combustion easily
prove, that the fat is wholly foreign to this want of colour of the
muscles examined in this state.
_Blood Vessels._
The arteries of the muscles are very apparent; they come from the
neighbouring trunks, penetrate the whole circumference of the organ,
more however towards its middle, than towards its extremities. They
run at first between the principal fasiculi, then divide and their
divisions go between the secondary fasciculi, subdivide and wind
between the fibres, and finally become capillaries and accompany
the small fibres, in which they deposit by the exhalant system the
nutritive matter. There are but few organs, which have, in proportion
to their size, more blood than the muscles.
The blood is essentially necessary to support their excitability, as we
shall see; it is that which colours the muscular texture, but not, as
it at first seems, by circulating in its texture. The circulating or
free portion contributes but little to it. It is the portion combined
with the muscular texture, that which contributes to its nutrition,
that gives it its colour; the following are proofs of it: 1st. The
fibres of the intestines are as much or more penetrated with the
circulating blood, than those of the muscles of animal life, and yet
their texture is evidently whitish, where these vessels are not found.
2d. Many animals with red and cold blood, frogs in particular, have
muscles almost white, and yet many red vessels run through this white
texture. 3d. I have observed that in animals destroyed by asphyxia,
the colouring substance does not change colour, no doubt because it is
slowly combined with the muscle by nutrition; that on the contrary, if
we cut a muscle of these animals in the last moments of life, whilst
the venous blood still circulates in the arterial system, this blood
flows out by black jets from the muscular arteries, the muscular
texture itself remaining red. This curious experiment, which I have
noticed in another work, is made by producing asphyxia in an animal by
compressing the trachea, or by intercepting the air in any other way in
this tube, whilst we examine the system of the muscles. When a muscle
has been exposed for some time to the contact of the air, to that of
oxygen especially, its red colour becomes evidently more brilliant.
The muscular vessels permit under certain circumstances the escape
of the blood they contain; hence different kinds of remarkable
hemorrhages, especially in scorbutic patients, sometimes in putrid
fevers, rarely or never in those diseases that are characterized by
an increase of vitality. Infiltrated with blood in preternatural
hemorrhages, particularly in false aneurisms, the muscles lose in
part their motion; this happens also in contusions, in which similar
infiltrations are observed.
The veins everywhere follow the arteries in the muscles; they have the
same distributions, and receive from the contractions of these organs
an essential assistance to their action. The throw of blood is more
powerful when the patient we have bled contracts his muscles, than
when he relaxes them; the fluid is as it were expressed, as from a wet
sponge which is squeezed. The arterial circulation does not exhibit
this phenomenon. I have observed that if we open the artery of the foot
of an animal, and by the irritation of the nerves, make the muscles of
the leg and thigh, through which this artery passes before reaching
the foot, contract powerfully, the throw of blood is not stronger than
during the relaxation.
I have many times injected the veins of the muscles of animal life with
ease, from the trunks towards the branches, which makes me believe,
notwithstanding what Haller has said, that in these organs, as in the
heart, the valves are less numerous than in many others. No doubt the
assistance the veins derive from their surrounding organs supplies the
place of these folds, or rather renders them useless, the weight of the
column of blood not making a great effort against the venous parietes.
The varices of the muscular veins are, as we know, extremely rare.
These veins are of two orders; one accompanies the arteries and follows
the same course, the others are spread superficially on the surface of
the organ, without having corresponding arteries.
There are absorbents and exhalants in the muscles; but we can with
difficulty trace the first, and the second cannot be perceived.
_Nerves._
Almost all the nerves of the muscles of animal life come from the
brain; the ganglions furnish a few of them; when this happens, as in
the neck, the pelvis, &c. besides the filaments coming from these
nervous centres, there are always filaments of cerebral nerves;
without this, these muscles would be involuntary. Few organs receive
more nerves in proportion to their size than the muscles. In general
the extensors appear to have rather fewer than the flexors; but the
difference is trifling. It is true that all the great nervous trunks
are in the direction of flexion, that in that of extension there are
only branches, as we see in the posterior part of the arm, of the
fore-arm, the vertebral column, &c. It is true also that this remark is
likewise applicable to the existence of the vessels, which are larger
and more numerous in the first than in the second direction; but this
greater number of vessels and nerves arises from this, that there are
many more flexors than extensors, that the first are stronger and have
more numerous fibres; so that each of these fibres hardly receives
more nervous or vascular filaments in one kind of muscles than in the
other. I think that there is but little foundation for what has been
said upon the difference of the strength of the fibres of the flexors
and of the extensors, upon the predominance of the first, &c. If these
are superior, it is either because they are more numerous, as in the
foot, the hand, &c. or more advantageously arranged, as in the trunk on
which the abdominal muscles act very far from the point of attachment
to bend the spine, whilst to extend it, the dorsal muscles exert their
action immediately at the side of this point of attachment, as also
in the neck, where the muscles that draw down the lower jaw and head
when this bone is fixed, are much further from the occipital condyles,
than the muscles which produce extension. Whatever may be the cause
of the superiority of the flexors, the fact cannot be doubted. 1st.
In hysterical convulsions, in those of infants, in all the spasmodic
motions in which the will has no part, the contractions take place much
more in the direction of flexion than in that of extension. 2d. In
old people the flexors finally become superior to the extensors; for
example, the fingers and toes are almost uniformly bent. 3d. In all the
motions, the power is always on the side of flexion.
The nerves enter the muscles of the extremities at a very acute angle,
because the nervous trunks are in the natural direction of these
organs. In the trunk, on the contrary, the nerves going from the spine,
the cervical especially, enter their muscles at almost a right angle or
one less evidently acute; this circumstance is of no importance. Each
branch in the fleshy fibres, is at first divided and then sub-divided
in their interstices, and afterwards lost in their texture. Does each
fibre receive a small nervous filament? We should be led to believe so
from this observation, that the principal branch being irritated, all
the fibres are put into action, no one remains inert. But on the other
hand, if we irritate one of them, all move also, which is certainly a
sympathetic phenomenon or one arising from the communication of the
cells.
Are the nerves deprived of their cellular coverings, and do they become
pulpy when they enter the muscles? Dissection has shewn me nothing like
it.