50 



HAND-BOOK OF PHYSIOLOGY. 



the foetal perichondrium and the periosteum of the adult are such as 

 usually exist between the embryonic and mature forms of connective- 

 tissue. 



Between the hyaline cartilage of which the foetal femur consists and 

 the bony tissue forming the adult femur, two intermediate stages exist 

 Tiz., calcined cartilage, and embryonic spongy bone. These tissues, 

 which, successively occupy the place of the foetal cartilage, are in suc- 

 cession entirely re-absorbed, and their place taken by true bone. 



The process by which the cartilaginous is transformed into the bony 



FIG. 53. 



FIG. 54. 



FIG. 53. Longitudinal section of ossifying cartilage from the humerus of a foetal sheep. Calci- 

 fied trabeculae are seen extending between the columns of cartilage cells, c, cartilage cells. X 140. 

 (Sharpey.) 



FIG. 54. Transverse section of a portion of a metacarpal bone of a foetus, showing 1, fibrous 

 layer of periosteum; 2, osteogenetic layer of ditto; 3, periosteal bone; 4, cartilage with matrix gradu- 

 ally becoming calcified, as at 5, with cells in primary areolae; beyond 5 the calcified matrix is being 

 entirely replaced by spongy bone. X 300. (V. D. Harris.) 



femur may be divided for the sake of clearness into the following six 

 stages: 



Stage I. Vascularization of the Cartilage. Processes from 

 the osteogenetic or cellular layer of the perichondrium containing blood- 

 vessels grow into the substance of the cartilage much as ivy insinuates it- 

 self into the cracks and crevices of a wall. Thus the substance of the car- 

 tilage, which previously contained no vessels, is traversed by a number of 



