OF CARTILAGE.
thickened, These cell-walls lie either in close contact, or have only a trace of intercellular substance between them, or there is sufficient of that material to entirely prevent the contact of the different cells. Their walls, which are originally formed of a very thin membrane, become thickened. The cavities of the cells with thickened walls which are seen in the centre of the branchial ray, are smaller than those of the cells which lie nearer the surface, the walls of which are less dense; but, whether this is produced by a thickening of the cell-wall taking place from without inwards, or whether rather the cells were not smaller in their original formation, is a matter of uncertainty. No deposition of strata, nor any distinction from the primordial cell-membrane, can be recognized in these thickenings of the walls. The condensed cell-walls at length coalesce either with each other, or with the intercellular substance, to form one homogeneous mass, in which only the cell-cavities remain perceptible, presenting the appearance of small distinct excavations filled with a transparent substance; these cell-cavities are the cartilage-corpuscles.
In the foregoing description no error can arise from the great variety in form which the cartilage-corpuscles frequently present; for, on examining the branchial rays of a very large pike, the gradual transition may be traced, from the thin-walled almost globular cells to the most varied forms, in which the remains of the cell-cavities are so much extended in length as to give to the cartilage almost a fibrous appearance.
The same extremely simple process of formation (modified, however, in some important respects) is presented in all cartilages. These modifications, the fundamental type of which is already pointed out in the cartilages of the branchial rays of fishes above described, depend chiefly upon the share relatively contributed by the thickened cell-walls, or the intercellular substance, to form the intermediate substance of the cell-cavities, or cartilage-corpuscles. We have seen that this intermediate substance was formed almost entirely of the thickened cell-walls, with but a minimum amount of intercellular substance, in the centre of the branchial rays of fishes, whilst at their base, that is, in the earliest formed cartilage, the intercellular substance preponderated, and the less dense cell-walls contributed less to the formation of the true substance of the cartilage.
