OSSIFICATION IN CARTILAGE. 



275 



matter in the matrix of the cartilage, the cells of which assume a highly charac- 

 teristic arrangement, and a deposition of true membrane-bone, underneath the 

 perichondrium, and closely investing the surface of the cartilage. 



What next happens is an irruption of the subperiosteal vascular and osteoblastic 

 tissue into the middle of the cartilage, one or more apertures being excavated by 

 absorption in the newly deposited osseous lamella and the tissue in question passing 

 through these and burrowing into the cartilage (fig. 312, ir}. Here it absorbs a 

 great part of the calcined matrix, and by demolishing in this way parts of the walls 



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Fig. 315. TRANSVERSE SECTION 



OF OSSIFYING CARTILAGE, IN- 

 CLUDING A PORTION OF THE 

 ADVANCING CALCIFICATION. 



FROM THE HUMERUS OF A 

 FCETAL SHEEP, MAGNIFIED 70 



DIAMETERS. (Sharpey. ) 



c, cartilage, the cells of which 

 are enlarged, but the matrix not 

 yet calcified ; b, primary osseous 

 deposit in the cartilage-matrix, 

 extending between the cartilage- 

 cells and enclosing them in 

 primary areolae. 



Fig. 



314. LONGITUDINAL SECTION THROUGH PART OF A PHALANX OF A 6 MONTHS' HUMAN EMBRYO. 



(Kblliker.) 



The calcified cartilage is completely absorbed almost to the limit of advancing ossification. The 

 darker substance on either side is the periosteal bone. The embryonic marrow has shrunk somewhat 

 away from it. 



of the primary areolse, forms larger spaces (the secondary areolce of Sharpey, the 

 medullary spaces of H. Miiller) which are filled by jelly-like embryonic marrow, with 

 ramified cells and osteoblasts, the cartilage-cells which occupied the primary areolae 

 disappearing before it. All the middle of the calcified temporary cartilage becomes 

 thus excavated with large spaces and replaced by the vascular osteoblastic tissue. 

 As the calcification of the cartilage-matrix extends towards the ends of the shaft, 

 proceeding always in the same manner, the osteoblastic tissue closely follows, and 

 after supplanting the cartilage-cells in the primary areolae, absorbs parts of their 

 walls so as to throw two or more together to form secondary areolae ; in this way a 

 great part of the primary bone (or calcified cartilage-matrix) is at once removed. 



At a short distance below the advancing ossification, the medullary spaces 

 become at first somewhat more enlarged by further absorption, but at the same time 



