THE BONES AND JOINTS. 741 



over an ill-defined and irregular area. The zoiie of calcification also, 

 instead of being narrow, regular, and sharply defined, is lacking in uni- 

 formity. Areas of calcification may be isolated in the region of prolifer- 

 ating cartilage cells, or calcification may be altogether absent over con- 

 siderable areas. 



Corresponding to these irregularities the ossification zone is also irreg- 

 ular. New-formed bone and marrow cavities containing blood-vessels 

 may lie in the midst of the cartilage, or masses of cartilage may lie deep 

 in the region which should be completely ossified. In other places it 

 seems as if the cartilage tissue were directly converted into an ill -formed 

 bone tissue by metaplasia or direct transformation. It will readily be 

 seen from this that the medullary spaces of the new-formed bone are 

 irregular, and this abnormality is enhanced by the premature intra-med- 

 ullary absorption of the bone. 



Similar irregularity in the bone formation may be seen beneath the 

 periosteum. An excessive proliferation of cells in the inner layers of 

 the periosteum, the irregular calcification which occurs about them, and 

 the absence of uniformity in the elaboration of ill -structured bone, con- 

 spire to produce an irregular, spongy bone tissue instead of the compact, 

 lamellated tissue which is so necessary here for the solidity of the struc- 

 ture. The increased cell growth between the epiphyses and diaphyses 

 produces the peculiar knobby swellings which are characteristic of rickets. 

 At the same time the medullary cavity increases rapidly in size and the 

 inner layers of the bone become spongy. The medulla may be congested, 





FIG. 490 RACHITIC BOXE. 

 Showing ossiHcation zone in a longitudinal section of a rib. 



and fat, if it has formed, may be absorbed, and a modified form of 

 osteitis may ensue. 



The result of these processes is that the bones do not possess solidity 



