86 



HISTOLOGY 



surface. Toward the area of resorption the osteoblasts become flatter 

 and less numerous, finally disappearing. 



In sections of bone, the places where resorption is going on may be 

 recognized by the presence of large multinucleate cells, which Kolliker 

 in 1873 named "bone destroyers" or ostodasts (preferably spelled osteo- 

 clasts). They are shapeless masses of protoplasm without any limiting 

 membrane, containing usually from one to twenty nuclei (Fig. 73). In 

 the largest of them, Kolliker counted from fifty to sixty nuclei. He 



Osteoblasts. 



Haversian canals in the 

 process of formation. 



Blood vessels. 

 Perichondrial bone. 



Finished Haversian 

 canal. 



Empty lacunae. 



Osteoclast. 



Endochondrial border- 

 line. 



Endochondrial bone. 

 FIG. 73- PORTION OF A CROSS SECTION OF A TUBULAR BONE OF A NEWBORN KITTEN. 



believed that they arose from osteoblasts through repeated nuclear di- 

 vision. Apparently they are not due to a fusion of cells; and they have 

 nothing in common, except their large size, with the giant cells of the bone 

 marrow, which will be described in connection with the blood. Osteo- 

 clasts are found along the surface of the bone, sometimes forming rounded 

 elevations or caps at the extremities of spicules, and sometimes imbedded 

 in shallow excavations known as Howship's lacuna. There seems to be 

 no satisfactory evidence that the osteoclasts are the active cause of bone 

 destruction. On the contrary they appear to be degenerating cells, pro- 

 duced by those conditions which lead to the dissolution of bone. 



