48 



CONNECTIVE TISSUE. 



adjacent cells, at right angles to these calcareous columns, lime 

 salts are also deposited, thus forming spaces containing cartilage- 

 cells, the boundaries of which are composed of the calcified matrix. 

 These spaces or cavities are primary areolce. While this process 

 is taking place at the center of the cartilage, beneath the mem- 

 brane which envelops the cartilage, the perichondrium, or, as it is 

 subsequently called, the periosteum, the osteoblasts form fibrous 



Vesicular cartilage- 

 cells. 



Primary periosteal 

 bone-lamella. 



_ Periosteal bud. 



Periosteum. 



Unaltered hyaline 

 cartilage 



FIG. 38. Longitudinal section through a long bone (phalanx) of a lizard embryo 

 (Bohm and Davidoff). The primary bone-lamella originating from the periosteum 

 is broken through by the periosteal bud. Connected with the bud is a periosteal 

 blood-vessel containing red blood-corpuscles. 



lamellae on the surface of the bone, which become calcified by the 

 deposit in them of lime salts. Some osteoblasts are closed in by 

 the lamellae and become bone-corpuscles. These changes which 

 take place on the surface beneath the periosteum constitute sub- 

 periosteal or intramembranous ossification, which has already been 

 described ; thus, both kinds of ossification take place in the long 

 bones. 



