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MESSRS. J. TOMES AND C. DE xMORGAN ON THE 
attention must now be directed to sections made across the bone, so as to cut trans- 
versely the lines of cartilage cells. 
If, then, we take a thin section through the cartilage where ossification of the inter- 
cellular tissue is advancing, the following appearances will be seen. The intercellular 
tissue will present itself in the form of more or less perfect septa lying between and 
enclosing the lacunal cells, in such a manner as to produce a uniform pattern over 
the surface of the section (Plate VIII. fig. 20). On close inspection it will be seen that 
the intercellular tissue is granular, and that in each enclosure it encircles one or two 
lacunal cells, which in the latter case lie in contact, with the contiguous sides 
flattened, while the peripheral surface of the two form together a tolerably perfect 
circle in close contact with the intercellular tissue. 
The lacunal cells are beautifully shown in the kind of section under consideration. 
Their circumference is becoming granular, and frequently may be seen as a perfect 
ring of granules in close contact with the intercellular tissue, while in the centre we 
see the granular cell with a well-defined nucleus, and with numerous rudimentary 
canaliculi, extending from the circumference of the inner cell towards the surface of 
the outer cell-wall. Where two cells lie in contact, the rudimentary canaliculi may 
sometimes be found running across from the one cell to the other. If after exami- 
ning such sections as may be made with a knife, we take one through the bone imme- 
diately below the partially ossified cartilage, rendered thin by grinding, and mount 
it in Canada balsam, the various points described as existing in ossifying cartilage 
will be seen in that which has been converted into bone. Thus we shall see the in- 
tercellular tissue preserving its original form, and highly granular, and that while the 
outer walls of the lacunal cells have become calcified, the granular cells will have 
assumed the form of perfect lacunae and canaliculi, the latter freely intercommu- 
nicating where the surface of the lacunal cells is in contact, but seldom extending 
into the ossified intercellular tissue. These conditions are shown in Plate VII. fig. 25. 
The ossified lacunal cells, and the intercellular tissue which have existed in the 
temporary cartilage, and have there served their part in forming the skeleton of the 
foetus, are destined to have but a short existence, for we find that no sooner is the 
bone formed than large spaces are produced by absorption. Whole lines of ossified 
lacunal cells with the enclosing intercellular tissue disappear, to be replaced by more 
or less perfectly developed Haversian systems, which also last but for a time, when 
they by a similar process are removed to give place to others, or to contribute to the 
formation of permanent cavities. It has been well stated by Dr. Sharpey, that the long 
bones of the foetus are not equal in size to the medullary cavities of the correspond- 
ing bones of the adult. Hence as growth takes place, gradually comes the necessity 
for the removal of parts to make way for the development of others upon an enlarged 
scale. 
It has been shown that primary bone, if we except two or three of the cranial 
bones, is merely calcified cartilage which has previously assumed the structural 
