THE CONNECTIVE TISSUES. 75 



niultiplv some of them become bone-corpuscles and through their 

 action new intercellular substances are produced. The marrow cavity 

 also enlarges. This is brought about by large multinuclear cells, 

 " osteoclasts," which cause the absorption of the intercellular sub- 

 stances of the bone with which they lie in contact, producing little 

 excavations, the Howship's foveolse or lacunae (Fig. 57). Through 



Fia 57. 



Lacuna ( . jmit ^ 

 / osteoclast) 



Vr^ ' s 



•?*—Bone 



Marrow cells 



*■«.. ---\ 



«• • • • •»** • ••■>•• 





G?'«»/ (W/ <&_ 



(osteoclast) .*• ' '•* 



From a longitudinal section of the femur of a rabbit's embryo. X 335. 



the agency of the osteoblasts and osteoclasts the bone is gradually 

 moulded to meet the demands upon it. In muscular individuals the 

 ridges and spines to which the tendons or muscles are attached 

 become larger and more prominent and the arrangements of the bony 

 plates in cancellous tissue are adapted to withstand the strains result- 

 ing from pressure bearing on the surfaces of the bones. The 

 eccentric larninse of bone already mentioned as existing between the 

 Haversian systems of compact bone are probably remains of former 

 complete systems which have been partially absorbed and replaced 

 by the existing systems of more recent production. 



