168 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



larity in the Cartilaginous tissue itself. In all considerable masses, how- 

 ever, we find a coarse network of canals, lined by an extension of the peri- 

 chondrium or investing membrane ; and these canals, which may be regarded 

 as so many involutions of the external surface, allow the vessels to come into 

 nearer relation with the interior parts of the Cartilaginous structure, than 

 they would otherwise do. They are especially developed at certain points, 



Fig. 66. 



Section of Cartilage at the seat of 

 ossification ; the clusters of cells are 

 arranged in columns ; the intercellular 

 spaces between the columns being 

 l-3250th of an inch in breadth. At the 

 lower end of the figure, osseous fibres 

 are seen occupying the intercellular 

 spaces, at first bounding the clusters 

 laterally, then splitting them longitudi- 

 nally and encirclingeach separate cell. 

 The greater opacity of this portion is 

 due to a threefold cause; the increase of 

 osseous fibres, the opacity of the con- 

 tents of the cells, and the multiplica- 

 tion of oil-globules. 



[Fig. 67. 



Vertical section of Cartilage near the surface of ossifi- 

 cation; 1, ordinary appearance of the temporary cartilage; 

 1', portion of the same more highly magnified; 2, the cells 

 beginning to assume the linear direction; 2', portion more 

 magnified; opposite 3, the ossification is extending in the 

 intercellular spaces, and the rows of cells are seen resting 

 in the cavities so formed, the nuclei being more separated 

 than above; 3', portion of the same more highly magnified. 

 From a new-born rabbit which had been preserved in 

 spirit.] 



which are to be the centres of the ossifying process ; and it is always observ- 

 able, that the vascularity is greatest at the zone, in which the conversion of 

 cartilage into bone is actually taking place. During the extension of the vas- 

 cular canals into the Cartilaginous matrix, certain changes are taking place 



