STRUCTURE AND DEVELOPMENT OF BONE. 
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arrangement of bone. It is proposed to restrict the term primary bone to tissue so 
formed, as it will be subsequently shown that the development of Haversian systems 
in the spaces formed in primary bone, is effected by processes similar to those which 
are concerned in the growth of bone generally, and in the extension of the flat cranial 
bones. Age and situation no doubt modify the conditions of growth, or development 
of secondary bone, as it may be called, but the processes in either case are alike. 
Hence, in describing the manner in which a long bone increases in diameter, we 
shall in fact be describing the process by which a flat cranial bone is extended. 
Before however going to this point the authors will state the results of their observa- 
tions on the subject of the absorption of bone, on that interesting and important pro- 
cess by which the Haversian spaces are formed out of the solid tissue of bone. 
During the present winter it became necessary to remove a portion of the femur 
which protruded from a stump six weeks after the removal of the limb. From the 
medullary cavity a granulating mass projected and covered the surface of the bone left 
by the saw, and as the bone was rapidly wasting from the inner or medullary surface, 
we had in this specimen a favourable opportunity of examining the tissue which lay 
in immediate contact with the surface of the wasting bone. On cutting through this 
piece of femur in its length with a very fine jeweller’s saw, it was found that a dense 
pale pink tissue lay in contact with the inner surface of the bone, which was hollowed 
with numerous minute cavities, into which the soft tissue accurately fitted, but from 
which it could be detached without tearing. The outer surface of the bone had been 
deprived of membrane many days before its removal from the limb. 
The examination of the tissue thus closely applied to the fast wasting bone, otfered 
as favourable an opportunity for learning something of the means by which absorp- 
tion is effected as we could reasonably expect to obtain, the more so since the 
outer surface having been for some time exposed and covered only by dried peri- 
osteum, the actions had been confined to the inner surface of the bone. A careful 
examination showed that the surface of this tissue was composed of minutely granular 
nucleated cells, which lay in close and immediate contact with the bone, and increased 
in an exact ratio with its diminution. What the bone lost in bulk the cells gained, 
the cellular mass presenting a perfect cast of the surface of the bone, suggesting to 
the mind that the soft was growing at the cost of the hard tissue, or at all events that 
the former was instrumental in the removal of the latter. The cellular mass was 
tolerably vascular, but the vessels did not reach the surface in contact with the bone ; 
hence they could not be regarded as having any immediate action in the process of 
absorption. Section of the bone showed that the medullary cavity had been greatly 
enlarged by absorption, and no doubt had sufficient time been allowed the femur at 
that part would have been reduced to a thin scale. A transverse section showed that 
in many, though not in all instances, the Haversian canals had been enlarged and 
rendered irregular in shape, but it was evident that the process of removal had been 
less active in this situation than on the medullary surface of the bone. 
