INTRA MEMBBANO US OS8JF11 'A TION 



43 



little from from those of white fibrous tissue. Like them, they are probably deposited in the matrix 

 through the influence of the cells in this case the osteoblasts. The osteogenetic fibres soon 

 assume a dark and granular appearance from the deposition of calcareous granules in the fibres 

 and in the intervening matrix, and as they calcify they are found to enclose some of the granular 



-a 

 ' <9 



J". 1<; . 11 -Longitudinal section through the second phalanx of the finger of a seven months' human embryo 

 btamed in hematoxylin and eosin. X 104. A. Periosteum. B. Primary areola. C Periodical bone D Sec- 

 ondary areola and marrow. E. Calcareous material. F. Endochondral bone. (Szymonowicz.) 



corpuscles, or osteoblasts. By the fusion of the calcareous granules the bony tissue again assumes 

 a more transparent appearance, but the fibres are no longer so distinctly seen. The involved 

 osteoblasts form the corpuscles of the future bone, the spaces in whjch they are enclosed con- 

 stituting the lacuna*. As the osteogenetic fibres grow out to the periphery they continue to 

 ossify and give rise to fresh bone spicules. Thus, a network of bone is formed, the meshes of 



E 



FIG. 12. Section through the red bone marrow of a rabbit. Biondi's stain. X 640. A Myelocytes 

 B. Eosinophiles. C. Nucleated red blood corpuscles. D. Giant cells. E. Myelocyte. (Szymonowicz.) 



which contain the bloodvessels and a delicate connective tissue crowded with osteoblasts. The 

 bony trabeculfe thicken by the addition of fresh layers of bone formed by the osteoblasts on their 

 surface, and the meshes are correspondingly encroached upon. Subsequently successive layers' 

 of bony tissue are deposited under the periosteum and around the larger vascular channels, 



