BONE. 



55 



triangular and resting against the strand of bone either by their base or 

 apex. They form bone only along that surface which is applied to the 

 matrix. As the strand of bone grows broader through their activity, it 

 encloses here and there an osteoblast which becomes thereby a bone cell 

 (Fig. 59). Apparently bone cells do not divide, and if they produce matrix, 

 thus becoming more widely separated from each other, it is only to a slight 

 extent and in young bones; they are therefore quite inactive. Each bone 

 cell occupies a space in the hyaline matrix, called as in cartilage, a lacuna, 



^ <^.4 



Osteoblasts. 



Haversian canals in 

 the process of for- 

 mation. 



Blood vessels. 

 Perichondral bone. 



Finished Haversian 

 canal. 



Empty lacunae. 



Osteoclast. 



Endochondral border- 

 line. 



Endochondral bone. 



FIG. 60. PORTION OF A CROSS SECTION OF A TUBULAR BONE OF A NEWBORN KITTEN. 



but unlike the lacunae of cartilage those in bone are connected by numerous 

 delicate canals, the canaliculi. In ordinary specimens the canaliculi are 

 visible only as they enter the lacunae, which are thus made to appear stellate. 

 The matrix around the lacunae resists such acids as destroy the ordinary 

 matrix and thus may be isolated in the form of "bone corpuscles." The 

 "corpuscles" correspond with the capsules of cartilage. The bone cells 

 nearly fill the lacunae and send out slender processes into the canaliculi. 

 These may anastomose with the processes of neighboring cells, as can 

 be seen in the embryo, but it is considered doubtful if this condition is 



