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. 1 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 long 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 

 fibrous tissue of the periosteum (or membrane covering the 

 bone) by calcareous deposit ; the lacunae being probably the 

 cavities of cells which were entangled in the fibres, and the 

 canaliculi 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- 

 laginous 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 

 a different process. In all bones of any considerable dimen- 

 sions, the process of ossification commences in more than one 

 point at a time. In the long bohes, there are usually three 

 such points; one for the shaft, and the others for the two 



1 It is commonly stated that the death of the anclers is due to the 

 formation of a bony ring at their base, which cuts off the supply of 

 blood from the " velvet" which covers them ; but though this may con- 

 tribute to produce the effect, it is by no means the sole cause, as the 

 interior of the antlers is supplied with blood from the vessels of the 

 bone from which they sprout, and not from those of the " velvet" 

 only. 



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