General Anatomy, Applied to Physiology and Medicine, Vol. 2 (of 3)

by Xavier Bichat

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.