206 



%vliich has been more recently put forward by Dr. Sharpey, that in 

 many cases it is composed of ossified decussating fibres. 



The authors have satisfied themselves that the ultimate structure 

 of bone tissue is composed of minute granules or granular bodies 

 imbedded in a clear or subgranular matrix ; and that the appearance 

 of fibres is dae in many cases to the mode of illumination. By 

 transmitted light passing through them in the long axis of the mi- 

 croscope the preparations show a granular or a structureless appear- 

 ance, or alternations of a granular and structureless part. But under 

 an oblique light passing from one side only an appearance of minute 

 flat fibres presents itself. This takes place even in the isolated cells 

 of old bone, or in developing young bone. This appearance is most 

 marked over the lacunae and canaliculi. But if a part which thus 

 appears fibrous be viewed under a hght passing obliquely from all 

 sides, as is effected by a Gillett's achromatic condenser, the fibres 

 disappear, and we see only a granular appearance, with some ten- 

 dency to arrangement in the granules. The fibrous appearance is 

 in fact due to the shadows cast from the less transparent parts when 

 the light passes obliquely, just as in the navicula the dots are re- 

 placed by lines. In thin sections torn from bone v/hich has been 

 macerated in acid, a reticulated appearance, similar to that figured 

 by Dr. Sharpey, may be seen, only however when the object is 

 slightly out of focus, or the light oblique and from one side. By 

 careful adjustment of the object-glass and of the illuminating appa- 

 ratus, this appearance may be shown to depend on the presence of 

 the canaliculi. 



8 and 9. Development and growth of bone. — The early condition of 

 cartilage, and the changes which take place in it and in the cartilage 

 cell before ossification, are particularly described ; and also the mode 

 by which they multiply and arrange themselves by segmentation, so 

 that a long column or cluster of cells represents an original cell, the 

 walls of which have coalesced with the surrounding hyaline tissue. 

 The cells at the same time enlarge individually as they approach the 

 point where ossification is going on, encroaching on the hyaline sub- 

 stance so as in many cases only to leave a fine line of intercolumnarv 

 tissue, or to cause it to disappear altogether. The nucleus at the same 

 time enlarges considerably, while the cell Avail becomes thickened 

 internally, until in the end it reaches the nucleus, which then be- 

 comes imbedded in firm tissue. Other changes now take place : 

 either several cells are thrown into one cavity by the absorption of 

 their contiguous w'alls, leaving the nuclei free in the common cavity ; 

 or the nucleus continues to occupy its parent cell, and sends off small 

 processes, which extend outwards to the cell wall. At this stage 

 the nucleus may be sometimes detached with the processes entire, but 

 generally it is adherent, and may be seen to have become a lacuna 

 with a central cavity and canaliculi ; in addition to which a nucleus 

 may be seen to occupy its interior ; it has in fact become a nucleated 

 cell, designated by the authors "granular cell." The entire cell may 

 now be detached from the intercolumnar tissue in which it lies. 



