Page 579 - My FlipBook

OSSIFICATION. 589

peared from the septa, and that the spaces which contained the large
granular cartilage-cells have become continuous with the advancing vas-
cular, bone-walled marrow-cavities, above described. It is to be dis-
tinctly understood that the calcifi-
cation zone is not bone, but only ^^^- ^^^
calcified cartilage, the true bone
being first fi_)rmed after this lime
has disappeared, on the surface of
the septa in which it was tempo-
rarily deposited—for what purpose
^ve do not know." (See accom-
panying figure, 328.)
The lengthening of the shaft pro-
ceeds until the cartilaginous head
itself becomes ossified, when all
further extension ceases and the
bones are said to be fully devel-
oped. This time varies in different
bones and also in the same class of
bones.
As regards the origin of the oste-
From Femur of Human Fcetus of 5 months (X
oblasts in the first instance I am '250): nc, normal cartilage; cc, calcified carti-
lage; lib, the dark line rt-preseuting developing
pretty fully convinced that they are bone; ?«/, marrow tissue.
the ordinary embryonic connective-
tissue cells. That this is so in the very early stages such as we have
described in interstitial development (p. 580) there seems to be no room
for doubt. The close intimacy between the vascular sujiply and ossifi-
cation tends to confirm the o])inion held by some, that they are modified
white blood-corpuscles. For my part, I see no antagonism between the
two theories above mentioned. I think it can be quite cleai'ly demon-
strated that even fixed connective-tissue cells' are only modified white
blood-corpuscles which have passed through several gradations governed
by location and environment, appearing (I.) as white blood-corpuscles
in the vessels; (II.) as escaped white blood-corpuscles; (III.) plasma-
cells ; (IV.) fixed connective-tissue cells. Ziegler has made extensive
studies in regard to the changes of the migrated white blood-corpuscles
into fixed connective-tissue cells in pathological conditions where there
is set up a process of progressive metamorphosis, and says that without
doubt such is the process of change.
Osteoblasts are a constant concomitant of bone-formation. Ossifica-
tion is a process which is under the superintendency of the osteoblasts.
We have seen that there exists an intimate relationship between the
vascular supply and calcification which precedes ossification. The
breaking down of the cartilaginous matrix is, without doubt, due to the
modifying influence of the capillary vessels. The hyaline l)asement-
substance is dissolved and the cartilage-cells are liberated. These carti-
lage-cells pass into the form of fibrillated connective-tissue cells from
which cartilage is originally developed.
The point I desire to make is this—that the white blood-cells are the
common basis from which the several members of the connective-tissue