THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 143 



deposit layers of calcium salts on the surface of the cartilage in the same 

 manner as around the trabeculae inside the cartilage. 



The transformation of the spongy bone into compact bone is peculiar 

 in that the former is dissolved and then replaced by new bone. Whether 

 this dissolution occurs through the agency of the large multinucleated cells 

 known as osteoclasts is not certain. By the process of dissolution the marrow 

 spaces are increased in size and are known as Haversian spaces. Within 

 these spaces new bone is then deposited layer upon layer, under the influence 

 of the osteoblasts, until the Haversian spaces are reduced to narrow channels, 

 the Haversian canals. The layers of bone are the Haversian lamella. The 

 interstitial lamella in compact bone have two possible origins. They may be 



Blood vessel 



Bone 



Cartilage 



Bone cell 



Cartilage cell 



Cartilage cell space 



Osteogenetic 

 tissue 



Osteoblasts 



FIG. 1 1 8. From same section as Fig. 115; showing bone deposited around one of the 

 trabeculae of cartilage. (Intracartilaginous ossification.) 



the remnants of certain lamellae of the original spongy bone which were not 

 removed in the enlargement of the primary marrow spaces, or they may be 

 parts of early formed Haversian lamellae which were later more or less 

 replaced by other Haversian lamellae. 



Carey, in his recent studies on certain mechanical phases of development, 

 concludes " that cartilage and bone are not self -differentia ted, nor are they 

 self-crystallized products," but represent " cellular responses to the varying 

 intensity of the stresses and strains produced by resistance (pressure) counter- 

 acting the growth" of the skeleton in its blastemal stage, that is, while the 

 cells are closely compacted prior to the appearance of the specific tissue. 

 In his analysis of the femur, Koch has concluded that the "normal external 

 form and internal architecture of the human femur results from an adaptation 

 of form to the normal static demands, or normal function of the bone." 

 It would appear therefore that in the development of bone mechanical factors 



