CH. V.] 



MARROW 



55 



marrow-cells are amoeboid, and resemble large leucocytes; the 

 granules of some of these cells stain readily with acid and neutral 

 dyes, but a considerable number have coarse granules which stain 

 readily with basic dyes like methylene blue. Among the cells are 

 some nucleated cells of the same tint as coloured blood-corpuscles. 

 These are termed erythroblasts. From them the coloured corpuscles 

 of the blood are developed. There are also a few large cells with 

 many nuclei, termed giant cells or myeloplaxcs (fig. 82). 



Yellow marrow fills the medullary cavity of long bones, and con- 

 sists chiefly of fat-cells with numerous blood-vessels ; many of its 

 cells also are the colourless marrow-cells first mentioned. 



Fie. 82. Cells of the red marrow of the guinea-pig, highly magnified, a, A large cell, the nucleus of 

 which appears to be partly divided into three by constrictions ; &, a cell, the 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. (E. A. Schafer.) 



Periosteum and Nutrient Blood-vessels. The surfaces of 

 bones, except the part covered with articular cartilage, are clothed 

 by a tough, fibrous membrane, the periosteum; and it is from the 

 blood-vessels which are distributed in this membrane, that the bones, 

 especially their more compact tissue, are in great part supplied with 

 nourishment ; minute branches from the periostea! vessels enter the 

 little foramina on the surface of the bone, and find their way to the 

 Haversian canals, to be immediately described. The long bones are 

 supplied also by a proper nutrient artery which, entering at some 

 part of the shaft so as to reach the medullary cavity, breaks up into 

 branches for the supply of the marrow, from which again small 

 vessels are distributed to the interior of the bone. Other small 

 blood-vessels pierce the articular extremities for the supply of the 

 cancellous tissue. 



Microscopic Structure of Bone. Notwithstanding the differ- 

 ences of arrangement just mentioned, the structure of all bone is 

 found under the microscope to be essentially the same. 



