BONE TISSUE. 



6r 



M .*- v,_ s <*>^ * 



----.. >> -_. 





Fig. 59- — Transverse section of a human 

 metacarpal bone ; a, outer surface ; c. medul- 

 lary canals with the special lamellae ; d, inter- 

 nal general lamellae ; e, bone corpuscles. 



are transversely or obliquely opened longitudinal canals. 

 Communicating horizontal canals are now also seen opened 

 in a longitudinal direction or 

 obliquely. 



The bone substance pre- 

 sents, as is shown by the 

 transverse section, a lamel- 

 lated structure. 



There is a double system of 

 layers, however. Firstly, we 

 meet with plates which pass 

 through the entire thickness 

 of the bone, in contact ex- 

 ternally with the periosteum 

 and internally limiting the 

 great medullary canals. They 

 are called general or funda- 

 mental lamellae {a, d). An- 

 other uncommonly abundant 



system of lamellae surround the individual medullary canals 

 with a varying number of layers. These are the special or 

 Haversian lamellae (around c). The thickness of both varieties 

 of lamellae varies from 0.0065 to 0.0156 mm., and the ar- 

 rangement is often far removed from making any claim to 

 regularity. This stratification may also be recognized in 

 longitudinal sections as a system of lines, though with less 

 distinctness. 



A plate of dry bone, let it be taken from where we will, 

 always presents a further extremely peculiar structural con- 

 dition ; it appears black by transmitted and white by incident 

 light, and consists of a marvellously complicated very fine 

 canal-work with indented and radiated nodal points. The 

 former passages are badly enough named calcareous canali- 

 culi : the dilatations bear the name of the bone corpuscles cr 

 lacunae (Figs. 58, 59). 



The form of the lacunae (Fig. 60, a) may be illustrated by 

 calling them lens-shaped, or by comparing them to the figure 



