THE TISSUES 



35 



known ; and how far it is dependent on the action of cells 

 has not been clearly determined. As a result of this, the 

 connective tissue cells get enclosed in definite spaces, 

 lacunae, and become bone corpuscles. Narrow branching 

 channels of communication 

 are left between theselacunae, 

 the canaliculi. This deposi- 

 tion of lime salts spreads out 

 irregularly from the centre 



into the adjacent fibrous **%* 



tissue. The fully formed 

 adult bone, however, is not 

 a solid block, but is com- 

 posed of a compact tissue 

 outside, and of a spongy bony 

 tissue, cancellous tissue, in- 

 side. This cancellous tissue 

 is formed as a secondary 

 process. Into the block of ^ 



calcareous matter, formed HHHI 

 as above described, processes 

 of the fibrous tissue, with 

 blood vessels, lymphatics, 

 and numerous cells, burrow. 

 This burrowing process 

 seems to be carried on by 

 the connective tissue cells 



which eat up the bony matter formed. In doing this they 

 frequently change their appearance, becoming large and 

 multi-nucleated. Thus the centre of the bone is eaten out 

 into a series of channels, in which the marrow of the bone is 

 lodged, and between which narrow bridges of bone remain. 



It is by the extension of the calcifying process outwards, 

 and the burrowing out of the central part of the bone, that 

 the diploe and cancellous tissue are produced. 



Intra-cartilaginous Bone Development. In the bones 

 preformed in cartilage, the process is somewhat more com- 

 plex, although all the bone is formed in connection with 

 fibrous tissue, the cartilage merely playing the part of a 

 scaffolding and being all removed. Where the adult bone 



FIG. 12. Intra - membranous Bone 

 Development in the lower jaw of a 

 foetal cat. Above, the process of 

 ossification is seen shooting out 

 along the fibres, and on the lower 

 surface the process of absorption is 

 going on. Three osteoclasts large 

 multi-nucleated cells are shown. 



