GROWING BONE. MARROW. 43 



it to the bone matrix. Where the spicular outgrowths of 

 the shaft are taking place, these fibrous connections are 

 evident, and numerous osteoblasts surround and lie amongst 

 their filaments. Osteoblasts are included at regular intervals 

 in the newly-deposited bony matrix (bone corpuscles). Observe 

 the gradual inclusion of the lacunae, and the formation of 

 the canaliculi as the deposition of bone proceeds. 



Ossification of the head takes place by a process closely 

 resembling that which occurs in the lifting zone below. The 

 cartilage capsules, becoming enlarged by proliferation of the 

 cartilage corpuscles and absorption of the intervening matrix, 

 are invaded by marrow; temporary cancellous tissue is formed, 

 which is ultimately replaced by erosion and surface deposition 

 of bone until only a thin layer remains upon the surface of 

 the head as articular cartilage and between the shaft and 

 head as the disc of lifting cartilage. The final union of. 

 the head and shaft takes place \vhen the lifting cartilage 

 disappears. 



Marrow. Carefully break up some red marrow in normal 

 saline. (//) Find the following: (a) Marrow cells proper 

 (Kolliker), a little larger than leucosites and with a large 

 round nucleus or sometimes two. (b) Erythroblasts smaller 

 than the last, nucleated, and having a reddish tinge in the 

 fresh state. () Large many-nucleated cells giant cells 

 (Myeloplaxes of Robin), these are in many cases osteoclasts. 



Red marrow. S. (p. 3., s. 22 & 24., c. P., m. B.) 1 Good 

 preparations will be obtained in young bones. (H) Find the 

 myeloplaxes and the other two varieties of cells. The sec- 

 tions should be very thin. Notice the wide thin-walled blood 

 vessels in its substance. 



1 Or marrow treated in Ranvier's alcohol and picroearmine and mounted in gly- 

 cerin jelly. Dried film preparations treated like blood films yield good preparations. 



