sacro-iliac symphysis which are found, though contiguous, unequal, rough, &c. We have also proved that this organic form is never owing to compression. From these different considerations we may be easily convinced, I think, that notwithstanding the adhesion of the synovial membrane at different points, it should be considered in a manner precisely analogous to that of the serous membranes, that is to say as a real sac without an opening, everywhere contiguous and spread upon all the organs of the articulation. Besides, do not the fibroserous membranes exhibit similar adhesions, though the separate existence of the two layers which compose them is generally admitted? From the idea we have formed of the synovial membrane, it is easy to conceive how certain organs pass through the articulation, without the escape of the synovia by the opening which receives or by that which transmits them. The synovial membrane then reflected around these organs, forms for them a sheath which separates them from the fluid and keeps them distinct from the articulation. Thus the tendon of the biceps is no more contained in the articulation of the arm with the scapula, than the umbilical vein, the urachus, &c. are in the peritoneal cavity. With the least care it may be separated from the portion of membrane which forms its sheath. The preceding considerations lead us also to find a perfect identity in the synovial capsules of the tendons and the articular synovial ones. In the preceding example, these two kinds of membranes are evidently continuous; for the capsule of the groove of the biceps is of the same nature as that of the tendons which have a separate one from it, as the flexors, for example. _Organization._ We have just seen, that the synovial membrane resembles very much in its external conformation the class of serous membranes, it does not less so in its internal organization. This organization is cellular, as is proved by dissection, inflation and especially maceration. The sac which the ganglions form is evidently only a production of the cellular organ; now it is known that this sac exhales and contains a fluid similar to the synovia. Wherever the synovial membrane is free, it is attached externally to this organ and is confounded with it in so direct a manner, that by raising successively its different layers they are seen to be gradually condensed and finally united together to form it. So that in the serous membranes no fibre is visible. It becomes transparent when it is separated accurately on both sides, which is easily done at the knee to a great extent.