Though the numerous organs which enter into this classification, belong to very different apparatus, though they seem to be spread here and there in the economy, without holding together at all, and though all appear insulated, yet they are almost all continuous and connected; so that we may consider the fibrous system, like the vascular and cerebral nervous systems, that is to say, as having a common centre, from which all the different organs go that form its divisions.
This common centre of the fibrous system appears to me to be the periosteum, not that I pretend that like the heart or the brain, it sends out radiations upon the organs that go from it, but because anatomical inspection shows us that all the fibrous organs are intimately connected with it, and by its means communicate with each other; the following observations are a proof of this.
1st. Among the fibrous membranes, that of the corpus cavernosum intermixes with the periosteum below the ischium; the dura-mater is continued with it through the foramina at the base of the brain; by uniting itself by the lamina which accompanies the optic nerve to the sclerotica, it joins to it this membrane, and thus serves as an intermediate organ for them. 2d. All the fibrous capsules above and below the articulation intermix with the periosteum. 3d. Wherever fibrous sheaths exist their fibres intermix with those of the periosteum. 4th. All the aponeuroses either of covering or insertion have a similar intermixing. 5th. Wherever the tendons are expanded, they are also confounded with this membrane. 6th. At the two extremities of the ligaments it unites also its fibres to theirs. There are none scarcely except the albuginea, the perichondrium of the larynx, the membranes of the spleen and the kidney, that form an exception to this general rule.
The fibrous system should be considered then in a general manner, that is to say, as extending itself everywhere, belonging at the same time to many organic apparatus, distinct in each by its form, but continuous in the greatest number, having everywhere communications. This manner of describing it will appear still more natural, if we consider that the periosteum, the general boundary of the different portions of this system, is itself everywhere continuous, and at the place where the articulations divide it, the fibrous capsules and the ligaments serve, as we have said, to reunite it.
We understand from this use of the periosteum in relation to the fibrous system, what the advantage is of its situation upon the bones which offer it a solid support, and give the same also to the organs of which it is the boundary.
ARTICLE SECOND.
ORGANIZATION OF THE FIBROUS SYSTEM.
In the midst of the varieties of form that we have just examined, the general organization of the fibrous organs is always nearly the same. I shall now consider this organization; I shall treat elsewhere of the varieties it experiences in each part. It arises from the union of a peculiar texture and of the vascular, cellular systems, &c.
I. Of the Texture peculiar to the Organization of the Fibrous System.
Every fibrous organ has for a base a fibre of a peculiar nature; hard, but slightly elastic, insensible, scarcely at all contractile, sometimes in juxta-position and parallel to each other, as in the tendons and the ligaments, sometimes crossed in various directions, as in the membranes, the capsules, the fibrous sheaths, &c. but everywhere the same, everywhere of a white or greyish colour, and of a remarkable resistance.