﻿Bones of the Skeleton as an Index of Nutrition. 209 



upon which a double role devolves — to produce osseous 

 tissue and to remove the embryonal cartilage. 



The cartilage matrix closing the enlarged cell spaces 

 next the primary marrow cavity suffers absorption, whereby 

 the cartilage cells are liberated, and the opened spaces are 

 converted into the secondary areolae, and directly communicate 

 with the growing medullary cavity. After the establish- 

 ment of this communication, the cartilage cells escape 

 from their former homes and undergo disintegration, taking 

 no part in the direct loroduction of the osseous tissue. 



Beyond the immediate limits of the primary marrow 

 cavity, the cartilage cells, in turn, repeat the preparatory 

 stages of increased size and impaired vitality already 

 described, but in addition they often exhibit a conspicuous 

 rearrangement whereby they form colunmar groups separated 

 by intervening tracts of calcified matrix. This characteristic 

 belt or zone of calcification surrounds the medullary cavity, 

 and marks the area in which the destruction of the cartilage 

 elements is progressing with greatest energy. 



" Simultaneously with the destructive phase attending 

 the absorption of the cartilage, the constructive phase is 

 instituted by the osteoblasts by which the bone tissue is 

 formed. These specialised connective tissue elements resting 

 upon the irregular trabeculae of the calcified cartilage bring 

 about, through the influence of their protoplasm, the deposi- 

 tion of a layer of bone matrix upon the surface of the 

 trabeculae, which thus becomes enclosed within the new bone. 

 After the latter has attained a thickness of at least the 

 diameter of the osteoblasts, some of the cells in closest 

 apposition are gradually surrounded by osseous matrix, 

 until finally they lie isolated within the newly formed 

 bone as its cells; the bone cells are, therefore, imprisoned 

 osteoblasts which in turn are specialised connective tissue 

 elements." 



We shall now consider, in the light of the theory of 

 growth, what all these extraordinary processes mean. 



(b) The Process of Ossification in Terms of the Theory of 

 Growth (see Fig. 2). — During the second month of intra- 



