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DEVELOPMENT OF BONE: OSSIFICATION. 65 
_ for the blood-vessels to pass along them. And it is through 
their complete blocking up, by a continuance of the same 
growth, that the supply of blood is cut off from the interior 
of the bone which forms the antlers of the deer, so that they 
die and fall off ; their shedding and renewal being an annual 
process.'— Whilst the formation of the Haversian canals and 
cancelli is being effected by the partial removal of the first 
formed partitions, a complete cavity is formed in the centre of 
the shaft of every Jong bone (at least in Mammals and Birds), 
by the entire removal of the solid tissue. This cavity is at 
first not much larger than one of the Haversian canals ; but 
as the bone grows in diameter by additions to the exterior of 
its shaft, so is the cavity in its interior augmented by the 
removal (by absorption) of the first-formed bone ; and this 
double process continues until the bone has attained its full 
diameter. The formation of new bone on the exterior of 
the shaft seems to be the result of the consolidation-of the 
rous tissue of the periosteum (or membrane covering the 
bone) by calcareous deposit; the lacune being probably the 
eayities of cells which were entangled in the fibres, and the 
‘analiculi being outgrowths from these; and new fibrous 
tissue being formed on the outside of the periosteum, to replace 
‘that which has been taken into the bone. Thus it comes to 
)pass, that after a time none of the bone first formed in its 
‘cartilaginous mould any longer remains, the whole of it 
‘having been removed by absorption ; since the central cavity 
‘of the perfect bone is much larger than the entire carti- 
Jaginous shaft in which it originated. And thus it also 
comes to pass, that (as gelatin is the basis of fibrous tissue) 
bones yield gelatin, not chondrin, upon being long boiled — 
The increase of the shaft in length, however, is the result of 
fa different process. In all bones of any considérable dimen- 
ions, the process of ossification commences in more than one 
doint at a time. In the long bones, there are usually three 
ich points; one for the shaft, and the others for the two 
_ 2 It is commonly stated that the death of the antlers is due to the 
formation of a bony ring at their base, which cuts off the supply of 
lood from the “ velvet” which covers them ; but though this may con- 
ibute to produce the effect, it is by no means the sole cause, as the 
erior of the antlers is supplied with blood from the vessels of the 
one from which they sprout, and not from those of the “ velve+” 
F 
