The free surface is constantly moistened by a fluid precisely similar to that of the articulations, furnished like it by exhalation, and not as authors have said by red bodies situated in the neighbourhood, bodies of which oftentimes there is no trace visible, and which, when they exist, have nothing glandular in them. This fluid is in general much less abundant than in the articulations, at least in the dead body. But there are varieties in the different synovial bags; those of the tendo Achillis, of the tendons of the psoas and iliacus united, of that of the obturator internus, &c. are always more moist than those of the flexor tendons, &c. Is it to the absence of synovia that must be attributed the species of crepitation which the tendons sometimes make in their motions? I know not. I would only observe that this crepitation has some analogy with the crackling noise of the joints of the fingers when they are bent quickly, a noise, which does not depend, as might be supposed, on the friction of the osseous surfaces; in fact, when it has been once produced, it cannot be again, though there may be friction again. Besides it is known that this crackling noise arises from the forced elongation of the phalanges, and consequently from the separation of their articular surfaces, as well as from the flexion. The increase of the fluid of the tendinous synovial membranes forms a species of dropsy which is called ganglion, a tumour which never exists in the synovial membranes of the fingers, no doubt on account of the want of extensibility of the fibrous capsules. It should not be thought however that all these tumours, which are cured by bursting them by strong pressure and thus effusing the fluid into the cellular membrane, have for their base a natural synovial membrane. Most frequently they are preternatural; they are cysts which are formed in the cellular texture. In fact these tumours are often found in the course of the great extensor of the thumb, where there is no synovial membrane. After rheumatic pains I have seen a considerable collection of fluid in the small synovial membrane of the tendo Achillis; it gradually disappeared. I have observed another analogous one in the bag of the psoas of a dead body. The fluid was reddish and of the consistence of currant jelly. The action of nitric acid immediately coagulated it into a white mass, analogous to the white of an egg hardened.