It appears that at the two extremities of the canal, the cells or membranes do not open into those of the texture of the cells, and that the medullary fluid of the preceding system does not communicate with the marrow of this. In fact, the line of demarcation which separates them is evident; they do not mix in a gradual manner. Air injected from one side of the medullary cylinder, only penetrates with difficulty and by tearing the membrane, into the texture of the cells of the opposite extremity of the bone; yet, notwithstanding these considerations, I confess that the question is not fully settled. The transudations in dead bodies have no influence in deciding it, on account of the permeability that our parts acquire after death. II. _Organization._ The texture of the medullary membrane is very little known, because its extreme tenuity conceals it from our researches; for it is only in the bones of ricketty subjects, that its morbid increase in thickness has permitted me to trace it accurately. It has the appearance of cellular texture; yet its properties and its nature are very different from this texture; it cannot be referred to any of the three classes of membranes, the serous, the fibrous or the mucous. Some have pretended that it was an expansion of the periosteum, which had passed through the numerous foramina by which the bone is perforated, and entered into the medullary cavity; but the least parallel made between these membranes is sufficient to make us see that they are essentially different in their functions, vital forces, &c. and cannot have the same texture. A principal vessel penetrates the medullary membrane; it is the artery, which enters by the only, but very large foramen, which is seen on the body of the long bones; the two branches of this artery and those of the corresponding vein, ramify in an opposite direction in the medullary cylinder, and by their innumerable branches give to it a very evident reddish colour, that disappears with age. The extremities borrow their vessels from those of the neighbouring texture of the cells. We cannot trace any nerve there. Such is sometimes the abundance of the fluids which penetrate this membrane, and its extreme tenuity, that it might be said not to exist. To be convinced of its existence, expose the cylinder that it forms to the intense action of heat; it contracts, has the horny hardening immediately like all the solids, and thus becomes more apparent. III. _Properties._ The properties of texture are very well marked in the medullary organ. 1st. The spina ventosa in which this organ is distended in a very evident manner with the body of the bone, proves its extensibility. 2d. The contractility of texture is made apparent by the contraction of the cells, after the amputation of the middle part of a long bone, a contraction which prevents the flow of marrow, which without it would take place on account of the communication of these cells.