266 



BONE OR OSSEOUS TISSUE. 



long bones in man it is of the character of ordinary adipose tissue, but the fat-cells 

 are supported by a kind of retiform tissue, and between them elements occur similar 

 to those immediately to be mentioned in the red marrow. In short bones, and in 

 the cancellated ends of long bones, but especially in the cranial diploe, the bodies of 

 the vertebras, the sternum, and the ribs, the marrow is red or reddish in colour, of 

 more fluid consistence, and with very few fat-cells. While, however, the fat-cells 

 are scanty in the red-coloured marrow, it contains numerous round leucocytes 

 the proper marrow-cells of Kolliker (fig. 307, e i)- These in general appear- 

 ance resemble the pale corpuscles of the blood, but are larger, with a clearer 

 protoplasm and a relatively larger nucleus. Like the pale corpuscles, they exhibit 

 amoeboid movements. Amongst them are smaller cells which have a reddish colour, 

 and resemble in appearance the primitive nucleated corpuscles of the embryo 

 (fig. 307, ;' t) ; these are the cells (erythroblasts) which are concerned in the 

 formation of the red blood-disks, and according to some authors are themselves 



Fig. 307. CELLS OF THE RKD MARROW OF THE GUINEA-PIG. HIGHLY MAGNIFIED. (E. A. S. ) 



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

 the enlarged nucleus of which shows an appearance of budding 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 undergoing division. 



derived from colourless marrow-cells or from pale blood-corpuscles (p. 219). It is, 

 however, doubtful if this is so ; it is more probable that they are the direct 

 descendants of the nucleated red corpuscles of the early embryo. Like these 

 they are amoeboid and divide by karyokinesis. They appear to be formed into 

 blood-disks by the disappearance of the nucleus and the moulding of the cell 

 protoplasm into the biconcave discoid shape. It is probably by virtue of their 

 amoeboid properties that they pass into the venous capillaries of the marrow, but 

 some may be contained within the vessels, and in birds all the erythroblasts are found 

 within the lumen of the venous capillaries (Bizzozero and Torre). 



Cells have occasionally been noticed containing one or more red corpuscles in their 

 interior (Osier) : whether these have been developed in situ in a manner similar to 

 that previously described in connective tissue corpuscles of the young animal, or 

 have been taken into the interior of an amoeboid cell, there to be transformed into 

 pigment-granules, is not certainly known. Cells containing reddish pigment- 



