314 



SPECIAL HISTOLOGY. 



many others where the cartilage ossifies only on one side, as in the con- 

 necting surfaces of the vertebrce. Where, however, the ossific nuclei in 

 the centre of a cartilage enlarge on all sides, the cartilage-cells are con- 

 fusedly grouped in roundish, or oval, irregular little masses, as in the 

 short bones at their first formation, and in the epiphyses. An accurate 

 comparison of the cells which are closer to the ossifying margin, with 

 those more remote from it, and of the groups formed by them, at once 



....<* 



shows that their particular disposition is directly related to their mode 

 of increase. Each individual group (or even two of them) corresponds, 



FiG. 130. Perpendicular section from the ossifying border of the shaft of the femnr of a 

 child a fortnight old : a, cartilage, in which the cells the nearer they are to the ossifying 

 border are placed together in more extended longitudinal rows ; 6, ossifying border, the dark 

 streaks indicate the progressive ossification in the intercellular substance, the clearer lines 

 the cartilage-cells which ossify subsequently; c, compact layer of bone near the ossifying 

 border; d, the substantia spongiosa formed in the osseous substance by resorption, with can- 

 celli, the contents of which are not shown. Magnified 20 diameters. 



FiG. 131. Femur of a child a fortnight old, natural size: a, substantia compact a of the 

 shaft; 6, medullary cavity; c, substantia spongiosa of the shaft; d, cartilaginous epiphysis with 

 vascular canals; e, osseous nucleus in the inferior epiphysis. 



