OF CARTILAGE.
minimum of salts, and gradually more and more, until the whole portion of cartilage obtains its due quantity; or, the earthy matter unites at first with some only of the smallest atoms of the cartilage, combining, however, with these to the full proportion which their capacity of saturation requires ; the remaining atoms then gradually and successively receive their due portion of the salts, so that each atom does not chemically combine with them until it can become completely saturated. The latter explanation, from the analogy with inorganic combinations, and from the above-mentioned granulous appearance which cartilage exhibits when undergoing ossification, appears to me by far the more probable. For, according to the first view, the medullary canaliculi, im the neighbourhood of which the deposition of earthy matter first commences, ought to be surrounded, not by a egranulous appearance, but by a dark shadow which should gradu- ally fade away to a pale edge.
I conceive the formation of the medullary canaliculi in ossifying cartilage to be similar to that of the capillary vessels, which will be examined hereafter. We shall return to them again, as also to the origin of the concentric laminae of bone.
We will now briefly sum up the observations upon cartilage, and refer to the phenomena of vegetable life, which either accord with or are dissimilar to them. Cartilage originates from cells, every one of which has its special, and, in the first instance, very thin wall; precisely like those of vegetables. These cells either lie closely together, and on that account are flattened against one another, like those of plants (see pl. I, figs. 5 and 6), or, there is intercellular substance present, and this again either in so very small a quantity as to be visible only in situations where three or four cells are in contact (see fig. 6, c), or in so much greater quantity, as to prevent the contiguity of the different cell-walls (pl. I, fig. 7; and pl. III, fig. 1.) Most of the cells, at their earliest period of development. (and per- haps constantly) contain a nucleus, that is, a round or oval, and sometimes hollow corpuscle (pl. I, fig.5, a; and pl. III, figs. 1 and 2), which again generally encloses one or two nucleoli. The cartilage-cells originate in the first place by the formation of the nucleus in the cytoblastema, around which the cell is afterwards formed, so that the latter at first closely encompasses the nucleus. The nucleus advances slightly in growth after the
