THE OSSEOUS SYSTEM. I 1 1 



increase in size. "When the branchiae have disappeared, all the 

 cartilage-cells are already quite transparent, with distinct nuclei 

 and walls, and they now gradually increase to the size of 0-018 — 

 002 4'", and the nuclei to that of 0-005 and 0-007'"; the cells, 

 from their mutual pressure, become polygonal, and constitute one 

 of the most delicate cellular tissues possible. They now also 

 begin to multiply by endogenous cell-formation around por- 

 tions of the contents (Nageli), so that in each cell two secon- 

 dary cells are formed around the two nuclei produced from the 

 original nucleus, and entirely fill it ; at the same time they 

 again increase, though very slowly, particularly in certain 

 cartilages of the head, until thev attain a size of 0013 — 

 0018"', and in some places of not more than - 006 — 013'"; 

 whilst between them, a thick interstitial substance is formed 

 out of the coalesced walls of the different generations of cells. 

 With respect to man and the mammalia, it can only be stated 

 as a supposition, that the cartilage- cells originate in a modifica- 

 tion of the primordial formative cells. This supposition is 

 favoured by the circumstance, that in a human embryo of eight 

 or nine weeks, the outer extremities of which were just deve- 

 loped, they presented scarcely a trace of formed cartilage, the 

 innermost cells of the rudimentary extremities being hardly 

 distinguishable from the outer. Thev were 0-004 — 0006'" in 

 size, spherical, with greyish granular contents, and indistinct 

 nuclei of 0003'", and formed a tissue of some consistence, 

 without any appreciable interstitial substance. The correspond- 

 ing cells in the embryo of a sheep 



6 — 7"' in length, were somewhat 



larger, although the embryo was 

 smaller than the human foetus above 

 noticed. In this case (fig. 129) they 

 measured, for the most part, 0006 — ^ 

 001 ", had distinct walls, nuclei, and 

 clear, aqueous, only slightly granular 

 contents, and were lodged in a scanty 

 homogeneous interstitial substance, so that they were only 



Fig. 129. Cartilage-cells from the humerus of an embryo of the Sheep, 6'" long : 

 a, cells with nucleus and clear contents (two cells retain remains of the earlier thick 

 contents); b, cells with consistent contents, without visible nucleus; c, intercellular 

 substance. 



