1 86 



PRACTICAL HISTOLOGY. 



[xiv. 



it calcified fibres of connective tissue, these covered with osteo- 



blasts (fig. 1 60). 



Marrow of Bone. It fills 

 the medullary cavity of long 

 bones, the cancelli of spongy 

 bone, and it occurs in some of 

 the larger Haversian canals. 

 There are two varieties, yellow 

 and red, the difference in 

 colour being due to the former 

 containing a large amount of 

 fat-cells. 



Yellow marrow occurs in 

 the medullary cavity or canal 

 and the larger cancelli of long 

 bones. Besides a small amount 

 of connective tissue and blood- 

 vessels, it consists principally of 

 fat-cells. 



Bed marrow (H) occurs in 

 the spongy tissue at the ends of 

 long bones, in the short bones 

 of the hands and feet, flat 

 c. Epiphy- b ones O f the skull, epiphyses of 



sial-cartilage ; 0. Bone; a. Row of carti- i i -i 



lage-cells; b. Cartilaginous trabeculre; m. long bones, clavicle, ribs, and 



Primary medullary space; n. Osseous ii moflnllarv rinal of tho 



deposit; V. Directive cartilaginous trabe- m l Jliary canal < 



culne ; p. Bone-corpuscle being embedded long bones of SO111C animals, e.<l.. 



iksviia TvioftMv / "\Tnr-pn\xr_r>^lla 11 . . 11- T 



guinea-pig, rat, rabbit. It con- 

 sists of delicate connective 

 tissue with blood-vessels and numerous cells of several varieties, 

 (i.) Medullary or Marrow Cells (fig. 161, a, b, c). They arc 



the most numerous, and are 

 nucleated cells, not unlike 

 large leucocytes. They are 

 spherical, with finely granular 

 protoplasm and a spherical 

 pale nucleus. Sometimes 

 they contain two nuclei. 

 Examined quite fresh in 

 serum, no nucleus is visible, 

 but it is revealed by the 

 action of acetic acid or 

 dilute alcohol. The proto- 

 plasm of some of them contains numerous highly refract! le granules, 

 and that of others some brownish granules. There is also a smaller 



FIG. 159. L.S. Head of a Metacarpal Bone of 

 Rabbit, aged three months. 



in the osseous matrix 

 Injected blood-vessel, 



c. Marrow-cells ; v. 

 240. 



Connective tissue bundle? 



Osteoblasts. Calcined. 



Non-calcified. 



FIG, 160. Surface Section of a Parietal Bone 

 Human Embryo x 240. 



