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MESSRS. J. TOMES AND C. DE MORGAN ON THE 
could not be rendered by a mere ag-gregation of soft cells, but are efficiently per- 
formed by the dense intercellular substance, which forms so characteristic a feature 
of the cartilage. Hence in the mechanical function of cartilage the intercellular 
element of the tissue must be regarded as the most important. 
A second, and scarcely less important purpose effected by temporary cartilage, 
is that of affording a medium for which a more solid tissue may be substituted, 
without the mechanical support being withdrawn from the adjoining parts during 
the process of change. It affords also a means by which the long bones are gradu- 
ally increased in length, without any interference with the functions of the limb. 
These changes are brought about by the g’radual increase in the numbei of the caiti- 
lage cells, at those parts only where ossification is about to commence, and by the 
conversion of the cells into lacunal cells, at the cost of the intercellular tissue, which, 
whilst its bulk is diminishing, becomes impregnated with the earthy salts ; so that 
although the quantity is lessened, the strength of that which remains is increased. 
Now, in examining the process by which growing bones are enlarged, it must be 
borne in mind that the mechanical function of the cartilage is performed by the 
bone which has replaced it, and that no such office is required of the new tissue 
which is gradually adding to the bulk of the bone. The necessity for a dense inter- 
cellular tissue no longer exists. Hence we have an aggregation of osteal cells with 
so much only of intercellular tissue as will serve to connect them into a mass. A 
certain number of these cells, by additions to their exterior, become lacunal cells. 
W Q have then in the place of lacunal cells and dense intercolumnar tissue, lacunal 
and osteal cells united by a small and almost imperceptible amount of a semifluid 
intercellular medium ; the relative proportions of these several parts varying a little 
with differences of age. Thus in aged subjects aggregations of lacunal cells may 
here and there be found with but few osteal cells and but little intercellular tissue, 
while in a young subject osteal cells will preponderate. 
In all cases a direction may be given to the cells of a growing part, by their being 
in relation with the insertion of a tendon. 
A consideration of the foregoing facts will, we think, lead to a conviction that the 
two different forms in which bone is developed, are designed to meet the require- 
ments of the animal at different periods of life, and that bone developed by means 
of osteal and lacunal cells is the higher form of the tissue. In early embryonic life 
a soft cartilaginous skeleton is laid down, which is hard as compared with the sur- 
rounding parts, and capable of affording them the required amount of mechanical 
support. As the various tissues advance in development the cartilage increases in 
density by the elaboration of its hyaline tissue, and after awhile those changes occur 
which precede its conversion into bone. But in the bone so formed, it has been shown 
that the canaliculi anastomose only at those points where the lacunal cells come into 
contact (Plate VHI. fig. 25 ). In bone formed from osteal and lacunal cells, the ana- 
stomosis of the canaliculi prevails throughout the tissue, while the outline of the 
