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lacunae or bone-cells, according as to whether they were ascertained 

 to be solid or hollow : these bone-cells, for this is the term which I 

 shall apply to them, have little tubes or canals radiating from them, 

 which are termed canaliculi by some authors, and tubes and pores by 

 others : those bone-cells which are nearest the Haversian canals have 

 the canaliculi of that side radiating towards and opening into the 

 Haversian canals, whilst the canaliculi of the opposite side communi- 

 cate or anastomose with those of the layer of canaliculi more external 

 to them, and those in the outer row have most of their canaliculi given 

 off from that side of the bone-cell which is nearest its own Haversian 

 canal ; hence arises the transparent white line which often may be 

 noticed as surrounding each concentric system of laminae and bone- 

 cells : in some cases, however, part of the bone-cells of the external 

 row anastomose with another series of bone-cells, which are situated 

 between the concentric laminae. The average length of the lacunae or 

 bone-cells in the human subject is the T oVoth of an inch : they are of 

 an oval figure, and somewhat flattened on their opposite surfaces, and 

 are usually about one-third greater in thickness than they are in 

 breadth ; hence, as will be presently shown, it will become necessary 

 to know in what direction a specimen is cut, in order to judge of their 

 comparative size. The older anatomists supposed them, from their 

 opacity, to be little solid masses of bone ; but if the section be treated 

 with spirits of turpentine, coloured with alkanet root, or if it have 

 been soaked in very liquid Canada balsam for any great length of 

 time, it can then be unequivocally demonstrated that both these sub- 

 stances will gain entrance into the bone-cells through the canaliculi. 

 The bone-cells, when viewed by transmitted light, for the most part 

 appear perfectly opaque, and they will appear the more opaque the 

 nearer the section of them approaches to a transverse one ; for when 

 the cells are cut through their short diameter, they are often of such a 

 depth that the rays of light interfere with each other in their passage 

 through them, and darkness results, whereas if the section be made 

 in the long diameter of the cells, they will appear transparent. When 

 viewed as an opaque object, with a dark ground at the back and con- 

 densed light, the bone-cells and canaliculi will appear quite white, 

 and the intercellular substance, which was transparent when viewed 

 by transmitted light, is now perfectly dark. It happens in most, if 

 not all, fossil bones, that the bone-cells, however much they may have 

 been soaked in turpentine, or even boiled in Canada balsam, are 

 nevertheless still opaque : this arises from the earthy matter, in which 

 they have been so long imbedded, having gained entrance into the 



