THE SKELET.VL SYSTEM 



199 



be clumped near the centre of the cell or may be arranged in a ring 

 or skein or irregularly In development of bone these cells appa- 

 rently have to do with its absorption. It is of interest to note that 

 they are also found at the roots of milk teeth which are being ab- 

 sorbed, and liilhoth describes them as apparently causing the 

 absorption of ivory pegs which had been driven into bone. 



Fat cells (p. 92), plasma cells (p. 89), mast cells (p. 89) and cells 

 of the reticular connective tissue (p. 99) are found in marrow in 

 varying numbers. 



^ 



'^ -:,. 



# 





m 





10 



•o;; M§^ 



•^ 



t 









M- 



. # 



# 



# 



%' 



#;:-' 



g f 



Fig. 119. — Section of Red Bone-marrow from Rabbit's Femur. X700. (Technic 

 4, p. 202.) a, Red blood cells; b, myeloplax; c, fat space; </, nucleated red blood cells; 

 e, myelocytes;/, reticular connective tissue; g, leucocytes. 



While all marrow contains the elements described, their propor- 

 tions vary greatly. Dependent upon the amount of fat present are 

 distinguished two main varieties of marrow, red marrow and yellow 

 marrow. 



Red marrow is found in all bones of embryos and of young ani- 

 mals, also in the vertebrae, sternum, ribs, cranial bones, and epiphyses 

 of long bones in the adult. In the diaphyses of adult long bones 



