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46 AXAT03IY

2d. Into this area blood-vessels enter from the under layer of the
perichondriiun (chondrogenetio layer), accompanied by osteoblasts (bone-
germs) and marrow-tissue.
Fig. 12.
As the vessels and osteo-
blasts advance into the
partly-absorbed cartilage, the
change of the cartilage is car-
ried on in front of them ; thus
the cartilage becomes chan-
nelled, forming cavities ir-
regular in shape named me-
dullary spaces. These are
lined by osteoblasts and in-
vaded or permeated l)y blood-
vessels and marrow-tissue.
3d. That poi-tion of the
cartilage basement-substance
which is not absorbed forms
irregular septa or trabeculse,
and is infiltrated with fine
particles of calcic salts, caus-
ing opacity and a granular
ajjpearance, M'hich, when cut,
has a gritty feel : this process
is called calcification, and is
an intermediate stage between
the absorption of the carti-
lage-matrix into medullary
spaces, and the ossification of
the bone by the infiuence of
the osteoblasts.
4th. The last stage, fol-
lowing closely that of calci-
fication, is called ossification
through the influence of the
osteoblasts. Portions of the
Section of Part of one of the Limb Bones of a Fa?tal Cat. -walls of the nicdullary SUaCCS
Tlie c:ilcitication of the cartilage-niatri.\ has advanced , i i i • j.
from the centre, and is extending between the groups of OCCOme abSOrbeCl, CaUSUlg tWO
caitilage-cells, whieli are arranged in characterisiic rows. ,-,, ,.^ ^C +K^ ,^,.;,itti.iV .no
The subperiosteal bony deposit {im) has extended pari Ol molC 01 lUe piUUai} lUL-
;i«.s-.vi/ with tlie Ciih'itica'tion of the cartilage-nuitrix. Tlie dullaiy spaces to become
cartiUitie-CfUs in tlie primary areol-.e are mostly shrunken
and steMatc; in some cases tlicy have iimppcd nut of the united and form secondary
.space. .\t /) and in two other places an irrujition of
the sul)periostc:il tissue, cuniiiosed of ramified ci'lls with spaces. In this way a great
osteoblast.s and growing blood-vessels, has penetrated the ' j. i? j.i • , - U -.nTi //->..
subperiosteal bony crust, and has begun to excavate the pari 01 Uie pnmai} OOUC ^^OI
secondary areola; or medullary spaces; i<, fihrous layer of nn^r^^f^aA r»ivtilnrrt> ni«itriv^ Jb
CaicmCCl
ic:
Cdl lliage-nUUl 1\)
the periosteum ; o, layer of osteoblasts -.some of them are
imbedded in the osseous layer as bone-corpuscles in jj^ OIK'C rcmOVcd.
lacnnie ; W, blood-vessels occupied by blood-corpuscles. ,, rr\ • j^ j_* j.
''
Turnuig our attention to
the exact wav in which bone is formed under the influence of the osteo-
bla.sts, we find tliat just beneath these cells, lying along the walls of the
new-formed medidlary spaces, the ba.sement-substance of true bone begins
to be deposited, at fir.'^t in the fi)rm of a narrow shell beneath each osteo-