CONVERSION OF CARTILAGE INTO BONE. 181 



bone, formed by the transformation of the intercellular substance be- 

 tween them. Immediately upon the ossifying surface, the nuclei, which 

 were before closely compressed, separate considerably from one another, 

 by the increase of material within the cells ; and the nuclei themselves 

 become larger and more transparent. These changes constitute the first 

 stage of the process of ossification, which extends only to the calcifica- 

 tion of the intercellular substance ; in this stage there are no blood- 

 vessels directly concerned. The bony lamellae thus formed, mark out 

 the boundaries of the cancelli and Haversian canals, which are after- 

 wards to occupy a part of the space that is hitherto filled by the rows 

 of cartilage corpuscles. 



302. Up to this point, there is no essential difference in the accounts 

 of those who have most carefully studied the process of ossification ; but 

 in regard to the history of its subsequent stages, there is much discre- 

 pancy ; and this especially with respect to the origin of the bone-lacunae, 

 which some regard as metamorphosed cartilage-cells, others as the spaces 

 originally occupied by their nuclei, whilst others do not regard them as 

 in any way derived from the cartilage-cells, but consider them as a new 

 formation. Much may doubtless be urged in favour of each view ; the 

 author's own observations incline him to the latter, and lead him to 

 regard the lacunas as cells, which, like the pigment-cells of Batrachia, 

 &c., have sent out the stellate prolongations that constitute the canali- 

 culi. All stages of gradation may be traced, between simple rounded 

 cavities, whose correspondence in size with the cells that are scattered 

 in the midst of the consolidating blastema leaves scarcely any doubt of 

 their identity with these, and the lenticular lacuna with numbers of 

 canaliculi proceeding from it. These gradations are particularly well 

 seen during the process of ossification ; so that it seems probable that 

 the radiating extension of the cells takes place during the consolidation 

 of the' surrounding tissue. It is an additional argument against the 

 idea that the bone-lacunae in any way originate from the cartilage-cells, 

 that they are found to present exactly the same characters in bone 

 which is developed in the substance of fibrous membrane (after the 

 manner to be presently described), and in the formation of which, there- 

 fore, cartilage has had no participation. 



303. Although, in a large proportion of the skeleton, the formation 

 of Bone is thus preceded by that of cartilage, yet such is by no means 

 invariably or necessarily the case ; for the flat bones, such as the scapula, 

 and those forming the roof of the skull, have usually only a centre of 

 cartilage, beyond which the ossifying process extends in membrane 

 only. This membrane is chiefly composed of fibrous fasciculi, corre- 

 sponding with those of the white fibrous tissues ; but amongst these are 

 seen numerous cells, some about the size of blood-discs, but others two 

 or three times larger, containing granular matter ; and a soft amorphous 

 or faintly granular matter is also found interposed amidst the fibres and 

 cells. The process of ossification here seems essentially to consist in 

 the consolidation of the fibres by earthy matter; for the first bony 

 deposit is seen as an irregular reticulation, very loose and open towards 

 its edges, and there frequently presenting itself in the form of distinct 

 spicula, which are continuous with fasciculi of fibres in the surrounding 



