470 Royal Society. 



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 light 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 which 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 groivth 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 intercolumnar 

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

 same time enlarges considerably, while the cell wall becomes thick- 

 ened internally, until in the end it reaches the nucleus, which then 

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

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

 their contiguous walls, leaving the nuclei free in the common cavity ; 

 or the nucleus continues to occupy its parent cell, and sends oflf 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. 



The granular condition of the intercolumnar tissue and of the cell 

 itself often renders the observation of this stage very difficult ; but 

 in rickety bone it is very readily shown, as in this disease there is a 

 tendency for the cells to assume their permanent form before the 

 deposit of bone-earth in any considerable quantity. To cells thus 

 composed of an outer thickened cell wall and an inner granular cell 

 (the cartilage nucleus of authors) which contains within it a nucleus 

 (the nucleolus of writers), which stands in the relation of a nucleus 

 to the future lacuna, the authors have given the name of " lacunal 

 cells," while the term granular cell has been applied to that which 



