OF CARTILAGE. 7s 
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 le 
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 per- 
ceptible, 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 carti- 
lages. 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 sub- 
stance, 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 sub- 
stance preponderated, and the less dense cell-walls contributed 
less to the formation of the true substance of the cartilage. 
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