ELEMENTS OF HISTOLOGY. [Chap. vii. 



channels grows more transparent, the lacunce becoming 



enlarged and the 

 cartilage cells more 

 transparent. The lat- 

 ter gradually break 

 down, while the in- 

 tercellular trabeculse 

 become calcified; 

 the lacuna? 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, and 

 into which project, 

 trabeculce of calcified 

 cartilage. The cavi- 

 ties 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 perios- 

 teum. (4) The os- 

 teoblasts arrange 

 themselves by active 

 multiplication as an 

 epitlteloid layer on 

 the surface of the 



calcined cartilage trabeculse projecting into, and bor- 



Fig. 34. Longitudinal Section through the 

 entire Foetal Humerus of a Guinea-pig. 



T, Periosteum ; J, hyaline cartilage of the epiphysis ; 

 c, intermediate cartilaere at the end of the shaft ; 

 tf, zone of calcification ; e.periostealbone.spongy ; 

 /, endochondral bone, spongy. 



