The cartilaginous system, like the osseous, is often developed in organs to which it is naturally a stranger. But there is this difference, that this phenomenon appears to be an effect of age in the first, whereas in the second it is always the effect of disease. Nothing is more common than to find cartilaginous balls in scirrhous, cancerous tumours, &c.; in the middle of those frequent morbid productions, in which the parts have an appearance like lard, in the lungs, liver, &c. when enlarged. I do not know why the peculiar membrane of the spleen has a great tendency to be encrusted with gelatine; it is perhaps of all the organs, that in which the preternatural cartilages are the most frequent. It is usually by irregular scales that the cartilaginous development appears; sometimes it attacks the whole membrane, which then presents a convex surface analogous to the convex surfaces of the moveable articulations, which the peritoneum covers, as these are covered by the synovial membrane. Can the spleen, when thus cartilaginous externally, yield to the changes of size that it often undergoes? I know not. We know that there are often moveable and loose cartilaginous substances in the articulations. Do they arise from the ossification of a portion of the synovial membrane? I presume they do; for we frequently see them hold to the cartilage by membranous expansions. I have seen in a dead body, within the last year, the portion of synovial membrane that goes from the fatty substance behind the patella, to the depression that separates the condyles of the femur, almost wholly cartilaginous. If during life it had been detached by the effect of the motions, it would have formed one of these moveable and loose cartilages. Besides, as I know but this fact which seems peculiarly applicable to this point, I can only offer conjectures, especially as we know that the synovial and serous membranes are of the same nature, and yet these last hardly ever become cartilaginous. Moreover these productions follow entirely the ordinary progress of ossification. At first cartilaginous and without blood vessels, they soon acquire a red centre, then osseous, which extends from the centre to the circumference, and which sometimes terminates by seizing upon the whole cartilage; so that they are real bones. This last circumstance is however very rare. The state in which we most commonly find these productions, is that in which they are osseous in the middle, and cartilaginous at the circumference. I found one of them in the articulation of the pisiform bone, of the size of the head of a great pin, and which, in its whole thickness was harder than ivory. FIBROUS SYSTEM.