82 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



cavation, begun by the cartilage cells, is -further en- 

 larged by the bone cells. The excavated areas are 

 now called the secondary areolce of Sharpey, the 

 cavities having a rich blood supply quite in con- 

 trast with the primary areolae. The marrow cavity 



Vesicular cartilage cells* 



Primary periosteal bone 

 lamella. 



Periosteal bud. 



Periosteum. 



Unaltered hyaline 

 cartilage. 



Fig. 50. Longitudinal section through a long bone (phalanx) 

 of a lizard embryo. 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 

 (Bohm and Davidoff). 



is excavated and the shaft becomes longitudinally 

 porous. Endochondral bone, therefore, develops in 

 cartilage, not from cartilage. 



5 . Osteogenetic cells attach themselves to the wall 

 of these enlarged Haversian canals and become en- 

 closed in lime deposits, forming thus the outer lam- 

 ellae and outer row of bone cells of each Haversian 



