BONE 



95 



B.V: 



FIG. 81. DIAGRAM OF THE DEVELOPMENT OF BONE. 



(In part, after Duval.) 



f., Fibrous layer of periosteum; o., osteogenic layer of peri- 

 osteum; os., osteoblast; b.c., bone cell; B. V., blood vessel; 

 H. C 1 ., beginning Haversian canal; H. C 2 ., complete 

 Haversian canal; i. 1., interstitial lamellae, c. 1., concen- 

 tric lamellae; Sh., Sharpey's perforating fibers. 



resorption, after which the deposition of bone is resumed. Resorption 

 lines are frequently seen in the Haversian systems (Fig. 80). 



Longitudinal sections of 

 decalcified bone show the way 

 in which the Haversian canals 

 connect with one another 

 (Fig. 82). The lamellae are 

 not so strikingly subdivided 

 into the groups seen in cross 

 sections, since both the con- 

 centric lamellae and the 

 ground lamellae are longitudi- 

 nal layers. The lacunae of 

 the Haversian systems, how- 

 ever, are flattened, parallel 

 with the course of the Haver- 

 sian canals, whereas those of 

 the interstitial lamellae are 

 more rounded or stellate. 

 The Haversian lacunas have been described as shaped like melon seeds. 

 Certain features of bone which can scarcely be seen in decalcified 



specimens are rendered 

 conspicuous in layers of 

 dried bone, ground upon 

 an emery wheel until 

 thin enough to be trans- 

 lucent. The Haversian 

 canals and lacunae with 

 the canaliculi projecting 

 from them, are then 

 empty, except for air 

 and particles of bone 

 dust. The specimens 

 are mounted in thick 

 balsam, which spreads 

 over the bone without 

 filling the lacunae and 

 canaliculi. When seen 

 under the microscope 

 these structures appear 

 black (Fig. 83), the air 

 within them being highly refractive. In such preparations the way in 

 which the canaliculi pass from one lacuna to another, their connections 



Periosteum. 



Fat .drops. 



FIG. 82. FROM A LONGITUDINAL SECTION OF A HUMAN META- 



CARPAL. X 3O. 



Fat drops are seen in the Haversian canals. At z Haversian canals 

 open on the outer, and at xx on the inner surface of the bone. 



