ELEMENTS OF HISTOLOGY. [Chap. vn. 



channels grows more transparent, the lacunae becoming 



enlarged and the 

 cartilage cells more 

 - o transparent. The lat- 

 ter gradually break 

 down, while the in- 

 tercellular tvabecu 1 se 

 become calcified; 

 the lacunae them- 

 selves, by absorp- 

 tion, fusing with the 

 cartilage channels. 

 These latter there- 

 by become trans- 

 formed into irregu- 

 lar cavities, which 

 are bordered by 

 projecting trabeculce 

 of calcified carti- 

 lage. The cavities 

 are the primary 

 marrow cavities, and 

 they are filled with 

 the primary or car- 

 tilage marrow, i.e., 

 blood - vessels and 

 osteoblasts, derived, 

 as stated above, from 

 the osteogenetic 

 layer of the peri- 

 osteum. (4) The 



Osteoblasts arrange 



themselves by ac- 



+i,, 



tlve 







in a 



on the surface of the 

 calcined cartilage trabeculae projecting into, and bor- 



Fig. 34. Longitudinal Section through the 

 entire Foatal Humerus of a Guinea-pig. 



a, Periosteum : 6, hyaline cartilage of the epiphysis ; 

 ,-, intermediate cartilage at the end of the shaft ; 

 d, zone of calcification ; e, periosteal bone.spongy ; 

 /, endochondral bone, spongy. 



