100 



BONE. 



FiiT. 59. 



In this view we see, at one part, the dark and nearly circular sections 

 of the newly-formed osseous areolEe ; at another, sections of the rows of 

 cartilage-cells with the clear matrix between and around tliem, and into 

 this the dark ossification is advancing. It may frequently be observed, 

 that here also, as in intramembranous ossification, the deposition of 

 calcareous matter is preceded by the formation of an obscurely fibrous 

 structure, extending between the rows of cells. 



On iising n higher jjower, as in fig. .59, it will 

 be seen that the cells forming the gi'oups are 

 jilacecl with their long diameter transversely, 

 as if they had been iiattened and piled iipon 

 one another ; but in the immediate vicinity of 

 the bone they become greatly enlarged and 

 more rounded. As to the substance composing 

 them, in some it is pellucid, strongly refract- 

 ing the light, and nearly filling the capsule ; 

 in others faintly granular and light like gi'ound 

 glass, and has a well-defined outline, and in 

 these there is a very distinct nucleus, varying 

 much in size in different cells, but always 

 most regularly circular, and inclosing one or 

 more nucleoli ; lastly, a good many cells may 

 be seen, esiiecially in the neighbourhood of 

 the advancing blood-vessels, in which the 

 contamed mass or cell-body does not nearly 

 fill the capsule, and then it is usually coarsely 

 granular, with an uneven and, in some, a 

 jagged outline. 



It thus appears that the bony tissue, as 

 it advances into the cartilage, has at 

 first a sort of alveolar structure, made 

 up of fusiform arcoke or short tubular 

 cavities, with thin parietes, which are 

 formed by calcification of the matrix 

 and partial calcification of the capsules 

 of the cartilage-cells. But this condi- 

 tion, which diifers from that of perfect 

 bone, is only transitory, and at a short 

 distance below the ossifying surface we 

 see a change taking place in the newly- 

 formed tissue ; the structure becomes 

 more open, the original cartilage-cells 

 disappear from its interstices, and the 

 medullary spaces, with their lamellated 

 parietes, as in the permanent cancellated 

 tissue, begin to be formed. This, which 

 is the next step of the process, takes 

 place in the following manner. The primar// areohc of the bone above 

 described open into one another both laterally and longitudinally by 

 absorption of their intermediate walls, and by their confluence give 

 rise to the larger or sprondary cavities, the methdlarii spaces of H. 

 Miiller, which succeed them lower down. This is shown in a longi- 

 tudinal section in fig. GO, and in transverse section in fig. Gl, a, 

 which represents a thin section made almost immediately below the 



/T^! 



Fig. 59. — Small Portion of a 

 Sectiox similap. to that in 

 Fig. 57, more highly magni- 

 fied (about 140 diameters). 



a, h, two of the new-formed 

 osseous tubes or areolfe, with a 

 few cartiliige-cells and granular 

 corpuscles lying in them ; c, c, 

 cartilage-cells near the ossifying 

 surface, exhibiting the appearance 

 described in the text. 



