OSSIFICATION IN CARTILAGE. 



101 



surface of ossification, and in which the primary cavities are seen to 

 have coalesced into larger ones. A transverse section somewhat lower 



Fig. 60. 



Fig. 60. — Thin Longitudinal Section op 

 THE Growing End of the Shaft of the 

 Metatarsal Bone of a Slink. Calf, mag- 

 nified. 



Tlie upper part of tlie figure shows four groups 

 of cartilage-cells, with calcified matrix between 

 them forming the walls of four primary areolae 

 filled as yet by the original cartilage-cells, 

 except at the lower part, where these are re- 

 placed by osteoblasts. Lower down are two 

 oblong spaces (secondary or medullary cavities) ; 

 one, indicated by d, is nearly filled by osteo- 

 l;)lasts and vessels, the other is vacant. The 

 walls of these spaces are beginning to be lined 

 with secondary osseous deposit, sho-w-n in the 

 figure as a lighter layer, 6, b, and b; c, c, and 

 c, are corpuscles about to be imbedded in the 

 ossifying substance and inclosed in laminre ; //, 

 a cartilage-cell of which the body has shrunk 

 from the inside of the capsule (after H. ]\Iiiller 

 and Kiilliker). 



down, (fig. 61, B,) shows that they go 

 on enlarging by further absorption 

 and coalescence, and that their sides 

 are thickened by layers of new bone ; 

 this soon begins to be deposited (fig. 

 GO, l>, h, in longitudinal and Gl, a, in 

 cross section), and goes on increasing, 

 (fig. CI, b). In the meantime the 

 cartilage-cells have disappeared, and 

 the bony cavities are filled with soft 

 matter, in which there are a few fibres 

 and numerous granular corpuscles re- 

 sembling the osteoblasts seen in the 

 intramembranous ossification ; there 

 are also many blood-vessels. In the 

 end, some of the enlarged cavities and 



open structure remain to form the cancellated tissue, but much of 

 this structure is afterwards removed by absorption, to give place to the 

 medullary canal of the shaft. In many of these cavities the walls of the 

 coalesced primary areola may long be distinguished, like little arches, 

 forming by their union a sort of festooned outline, within which the new 

 bony lamina are situated. 



Tlie primary osseous matter forming' the original thin walls of the areolae, and 

 produced by calciUcation of the cartilaginous matrix, is decidedly granular, and 

 has a dark appearance ; the subsequent or .wcondary dcjjoxit on the other hand is 

 quite transparent, and of a uniform, homogeneous aspect. This secondary 

 deposit begins to cover the granular bone a very short distance (about ith of an 

 inch) below the surface of ossification, and. as already stated, increases in thick- 

 ness further down. The lacunjB first appear in this deposit ; there are none in 

 the primary granular bone. The cartilage-cells do not become calcified. According 

 to H. Muller the capsules are opened by absolution, and the granular bodies con- 

 tained within them {iu: the proper cell-bodies) produce by fissiparous multiplication 



