68 NORMAL HISTOLOGY. 



periosteum is attached to the bone by connective- 

 tissue fibres, which pass from the former into the 

 substance of the latter, the attachment being firmer 

 at some points than at others, as, for example, near 

 the extremities of the long bones and at the points 

 of insertion of the tendons and ligaments. Blood- 

 vessels pass also from the periosteum into the 

 bone. 



3. Marrow. Marrow-tissue is found in the cen- 

 tral or medullary cavity of bones, in the tiny cham- 

 bers of spongy bone, and in the Haversian canals. 

 Sometimes it has a yellowish color and is fatty, 

 sometimes it presents itself in the form of a red- 

 dish pulp. Red marrow is found in embryos and 

 in young animals, and in adults in certain small 

 bones and in vertebrae. In certain animals, such as 

 the rabbit and guinea-pig, red marrow is found in 

 most of the bones, even in adult life. In adult 

 man, under normal conditions, the marrow except 

 in the vertebrae, ribs, and certain small bones is 

 yellow. Yellow marrow differs from the red in 

 that it contains a large amount of fat, sometimes 

 consisting almost exclusively of fat-cells. 



We find in red marrow, which is best adapted for 

 study, blood-vessels and spindle-shaped or branching 

 cells, which constitute the supporting framework of 

 the tissue! In the interstices of the latter lie sev- 

 eral distinct kinds of cells: I. Fat-cells; 2. smaller 

 and larger spheroidal cells, having essentially the 



