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 



Periosteal bud. 



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. Kndochondral 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 



