Why are the fibrous capsules found only around the first kind of articulations? The reason of it is plain; as these articulations have in all directions motions nearly equal, they should have on all sides an equal resistance, whilst the others moving in one or two directions only, the ligaments were unnecessary except at certain places, to limit these motions. Hence why for example, the fibrous system is spread out like a membrane around the ilio-femoral articulation, and collected into distinct fasciæ around the femoro-tibial, where the synovial membrane is almost everywhere bare. We understand from all that has been said, that the only use of the fibrous capsules is to strengthen the articular relations, and that this use has no connexion with synovial exhalation. When in luxations not reduced, the head of the bone has left the articular cavity, a new membrane is formed around it in the cellular texture which serves for a capsule; but this membrane has not the texture of the former one. I have observed in two subjects, that no fibre could be distinguished in it, that its texture was very analogous to that of the different cysts that are often found in many parts of the economy, of those especially that form round foreign bodies, the presence of which is not a cause of suppuration, and that consequently these preternatural capsules belong rather to the class of serous than to that of the fibrous membranes. ARTICLE SEVENTH. OF THE FIBROUS SHEATHS. The fibrous sheaths are, as we have said, partial or general. I. _Partial Fibrous Sheaths._ The partial sheaths destined to a single tendon are of two sorts; one runs a long course; such are those of the flexors of the foot and the hand, which correspond to the whole concave surface of the phalanges; the others form only a kind of rings, in which a tendon is reflected, an example of which is seen in the great oblique muscle of the eye. All in general form a semi-circle and make half of a canal which the bone completes; so that the tendon slides in a canal half osseous and half fibrous. This canal is lined by a synovial membrane, the attachment of which to the fibrous sheath is equal to that of the articular synovial membrane to its capsule. By their external surface, the fibrous sheaths correspond with the neighbouring organs, to which they are united by a loose cellular texture. All these sheaths are of a very dense and compact texture; they are stronger in proportion to the effort which the tendons can exert upon them, than the fibrous capsules are in relation to the different impulses which the bones can communicate to them and which tend to rupture these capsules. They are confounded with the periosteum at their two edges. Those of the flexors unite also by their extremity with the expansion of the tendons; hence the very considerable fibrous interlacing that is observed at the extremity of the last phalanges.