62 



THE ESSENTIALS OF HISTOLOGY. 



of osteoblasts or lone-forming cells, a remainder of those which originally 

 produced the bone. 



The marrow of bone is of a yellow colour in the shafts of the long 

 bones, and is there largely composed of adipose tissue, but in the can- 

 cellated tissue it is usually red, the colour being partly due to the large 

 amount of blood in its vessels. This red marrow is chiefly composed of 

 round nucleated cells the marrow-cells (tig. 72,e-i) which resemble large 

 lymph-corpuscles, and, like these, are amoeboid. There are also to be 

 seen mingled with them a number of corpuscles somewhat smaller in 

 size, but nucleated and amoeboid, and of a reddish tint (fig. 72, j-t). 

 These cells, which are termed erythroblasts, resemble the nucleated 



FIG. 72. CELLS OF THE RED HARROW OF THE GUINEA-PIG. (Highly magnified.) 



, a large cell, the nucleus of which appears to be partly divided into three by constrictions ; 

 b, a cell the enlarged nucleus of which shows an appearance of being constricted into a 

 number of smaller nuclei ; c, a so-called giant-cell or myeloplaxe with many nuclei ; d, a 

 smaller myeloplaxe with three nuclei ; e-i, proper cells of the marrow ; j-t, various forms of 

 coloured nucleated cells, some in process of division. 



coloured blood-corpuscles of the embryo, and they are believed to be 

 cells from which the coloured blood-disks become developed (Neumann). 

 Many of them are in process of division by karyokinesis, and others are 

 seen with the nucleus in a more or less atrophied condition ; from 

 which it may be inferred that the transformation into a discoid blood- 

 corpuscle is accompanied by the disappearance of the nucleus 

 (Bizzozero). Lastly the marrow contains a certain number of very 

 large cells with multiple nuclei, the myeloplaxes of Robin (fig. 72, 

 a, b, c, d). These are especially numerous wherever bone is becoming 

 absorbed, but are not confined to such situations, being indeed normal 

 constituents of marrow. Sometimes, instead of possessing several 



