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

by Xavier Bichat

I. Form of the Tendons.

Usually situated at the extremities of the fleshy fascia, they sometimes however occupy the middle, as we see in the digastric muscle; they are almost always found at the most moveable extremity, that which serves for support having aponeuroses for insertion, as we see especially on the fore-arm and the leg, of which all the muscles inserted above by broad osseous or aponeurotic surfaces, terminate below by a more or less slender tendon. From this arrangement result, 1st, little thickness at the extremity of the limbs, and consequently facility in their motions; 2d, great resistance to external pressures very frequent in this place, the fibrous texture being, as we have said, very resisting; 3d, the concentration of the whole effort of a muscle oftentimes very thick upon a very narrow osseous surface, and for the same reason the extent and force of the motions of the bone.

The tendinous forms are usually round, no doubt because they are those in which, with the least size the greatest quantity of matter enters. Sometimes however as in the tendons of the extensors of the leg and the fore-arm, they are flat.

Sometimes bifurcated or divided into many secondary elongations, the tendons are inserted into the bones, or receive fleshy fibres in two or many different points. All are covered by a loose texture which allows them to slide easily upon each other, or upon the neighbouring parts. Sometimes this texture is wanting, and then the synovial capsules surround them to favour their motions. Their extremity, in which the fleshy fibres are fixed, receives these fibres differently. Sometimes it is to one side only that they are attached; hence the semi-penniform muscles; at other times it is to both sides at the same time; this constitutes the penniform. Frequently the tendon is buried so deep in them, that it cannot be laid bare, but by dividing them longitudinally.

The adhesion is very great between the fleshy and tendinous fibre. Yet by macerating them a long time or subjecting them to ebullition, they gradually separate from each other. I have observed that in young subjects the union was much less intimate; thus by scraping at this age the tendon with a scalpel, we remove from it the muscle, without its ever appearing again; the polish is almost the same where the fibres are inserted, as where they are naturally wanting. The extremity of the tendon fixed to the bone, intermixes with the periosteum as it usually expands; so that it is with this membrane, and not with the bone itself, that the tendon makes part, because in fact it is the membrane which is of the same nature; thus if it finds an analogous membrane, it fixes to it equally, as we see in the insertion of the straight and oblique muscles in the sclerotica, of the ischio and bulbo-cavernous ones in the membrane of the corpus cavernosum. In general the tendons never unite but to fibrous membranes; the serous, the mucous, every organ in a word, foreign to the fibrous system, is also heterogeneous to them.

II. Organization of the Tendons.

The fibrous texture is extremely compact in the tendons; many appear homogeneous at first view; but by examining them with care, we soon distinguish fibres, connected by a small quantity of compact cellular texture. Ebullition renders these fibres very evident; when we plunge suddenly the tendon into boiling water at the place where it has been cut transversely, they become a little thicker at this divided extremity, swell as it were and are thus very evident. At the place where they expand to form an aponeurosis or to unite to the periosteum, these fibres can be distinctly seen without any preparation. On the other hand, as we can always, as I have said, reduce artificially a macerated tendon to an aponeurosis, and as in this state of maceration, soft and loose, it yields to all the forms we wish to give it, it is an excellent means of distinguishing the tendinous fibres. In this experiment so easily repeated, I have never seen the spiral form of the tendinous cylinders, of which some modern authors have spoken. These fibres are in the tendon as at the place where they separate to form an aponeurosis, that is to say in a right line.

Blood scarcely enters the vascular system of the tendons; but in some inflammations, they are wholly penetrated by it. I have seen one of those of the extensors, laid bare in a whitlow, so red, that it had the appearance of a phlegmon. Yet I observed that this colour was not, as in many other inflamed organs, dependant on the small red striæ, an indication that the exhalants are filled with blood; but it was uniform, as for example a body dyed red. In general, it appears that of the whole fibrous system, it is the tendons which have the least energetic degree of vitality, and the most obscure vital forces. By dissecting them in a living animal I have found that they have exactly the same arrangement as in the dead body; the white fluids that penetrate them do not flow under the scalpel; they are dry and can be removed by layers. They appear to have a very low temperature; for, in general, the degree of heat of an organ is in proportion to the quantity of blood vessels it receives.

If in the body they are at the general temperature, it is only because the neighbouring organs communicate theirs to them. Caloric is not disengaged in their texture.

The tendons have a remarkable affinity to gelatine and even the phosphate of lime; where they slide upon a bone, and where they suffer a great friction, they exhibit a hardness which authors attribute to pressure, by comparing it to the callous hardening of the sole of the feet, but which is owing evidently to an exhalation in the tendinous texture of the two preceding substances, an exhalation which the motion produces and from which arises a real ossification.