OSTEOLOGY I? 



tractive matter. In the flat and short bones, in the articu- 

 lar ends of long bones, in the bodies of the vertebra, in 

 the cranial diploe, and in the sternum and ribs it is of 

 red color, and contains 75 per cent, water, 25 per cent, of 

 solid matter, consisting of albumin, fibrin, extractive mat- 

 ter, salts, and a mere trace of fat. Marrow possesses 

 five kinds of cells: fat cells, marrow cells proper, resem- 

 bling leukocytes, nucleated red cells, cells containing red 

 corpuscles, and giant cells. 



Vessels of Bone. The blood-vessels of bone are 

 very numerous. Those of the compact tissue are de- 

 rived from a close and dense network of vessels ramifying 

 in the periosteum. From this membrane vessels pass into 

 the minute orifices in the compact tissue, running through 

 the canals which traverse its substance. The cancellous 

 tissue is supplied in a similar way with a less numerous set 

 of larger vessels. In the long bones numerous apertures 

 may be seen at the ends near the articular surfaces, which 

 give passage to the vessels referred to; but the most nu- 

 merous and largest apertures are for the veins of the can- 

 cellous tissue, which run separately from the arteries. 

 The medullary tissue of all long bones receive a good-sized 

 artery (the medullary artery), which obliquely pene- 

 trates the compact tissue at the nutrient foramen, after 

 which it divides into two main branches, one ascending, 

 the other descending, in the medullary canal; the veins 

 chiefly emerge through numerous openings near the articu- 

 lar ends of the bones, and form the nutrient foramen. 

 Nerves are distributed freely to the periosteum, and ac- 

 company the nutrient arteries into the interior of the 

 bone. 



Haversian Canals. The Haversian canals run 



parallel with the longtiudinal axis of the bone for a short 



distance, and then branch off and communicate with 



others. As seen in cross-section in Fig. i they appear 



2 



