OSTEOID TISSUE. 459 



small, cellular elements ; the farther we recede from the 

 bone, the more do divisions of cells occur, and at last 

 we meet with the simple, very small connective-tissue- 

 corpuscles of the periosteum. The division follows the 

 same course as in cartilage, only that the dividing cells 

 of the periosteum are very delicate. The greater the 

 irritation, the greater also the proliferation, and the 

 more considerable the swelling of the growing spot. 



The cells which thus result from the proliferation of 

 the periosteal corpuscles are converted into bone-cor- 

 puscles exactly in the way I described when speaking 

 of the marrow. In the neighbourhood of the surface of 

 the bone the intercellular substance grows dense and 

 becomes almost cartilaginous, the cells throw out pro- 

 cesses, become stellate, and at last the calcification of 

 the intercellular substance ensues. If the irritation is 

 very great, the corpuscles grow very considerably, and 

 then real cartilage is produced ; the corpuscles enlarge 

 to such an extent that they grow into large, oval or 

 round cells, and each of these forms a capsule around 

 itself by secretion. In this manner cartilage may arise 

 in the periosteum also, by means of a direct transforma- 

 tion of its proliferating layers, but it is by no means 

 necessary that real, true cartilage should be produced ; 

 generally only the osteoid transformation takes place, 

 when the intercellular substance becomes sclerotic and at 

 once calcifies. 



Thus it is, that on the surface of every growing bone, 

 as Flourens particularly has shown, new bone is continu- 

 ally deposited layer after layer, and that the new layers 

 grow round the old bone in such a way, that a ring, 

 which is early put around the bone, after a time lies 

 inside it, enclosed by the young layers which have 

 formed outside around it. These are connected with 

 the old bone by means of little columns which give the 



