SO CONNECTIVE TISSUE CARTILAGE BONE 



much later than that for the shaft of the bone, for the most part not 

 until some mouths after birth, and from an extension of marrow from 

 the primary center. 



Enlargement of the Cartilage Cells. The first indication of begin- 

 ning bone formation is evidenced by an enlargement of the cartilage cells 

 which promptly arrange themselves in rows or columns that radiate from 

 the center of ossification (calcification). This process is accompanied 

 by absorption of the adjacent cartilage matrix, so that the enlarged car- 



C 



FIG. 91. THE PRIMARY CHANGES IN INTRACARTILAGINOUS BONE FORMATION. 



A, metatarsus; B and C, phalanges of human fetus. In A, the earliest enlarge- 

 ment of cartilage cells at the center of ossification is shown. B and C are successively 

 later stages. The bones are cut in longitudinal section. Carmin hematoxylin stain. 

 X 27. (After Toldt.) 



tilage cells are contained within broad spaces or areolce. The cartilage 

 cells now appear to undergo a gradual but progressive absorption ; their 

 cytoplasm becomes shrunken and granular and finally disappears, even 

 the nucleus at last succumbs to the process. 



Calcified Cartilage. The absorption of the cartilaginous matrix pro- 

 ceeds more rapidly in those portions which separate the individual cells 

 in the columns than in those other portions which intervene between 

 the adjacent rows of cartilage cells. While the former portions are 

 entirely absorbed, remnants of the latter remain, and in them calcium 

 salts are deposited in an irregular manner. Calcified cartilage, the most 

 primitive of the calcareous tissues, is thus formed. 



