BONE. 59 



the shaft of a long bone they are seen as small rounded or irregular 

 holes (fig. 66). When the section has been made by grinding, the 

 holes get filled up with air and debris, and they then look black by 

 transmitted light, as do also the lacunae and canaliculi (fig. 67). Most 

 of the lamellae in compact bone are disposed concentrically around the 

 Haversian canals ; they are known as the Haversian lamellae, and with 



FIG. 67. TKANSVEESE SECTION OF COMPACT TISSUE (OP HUMEEUS.) (Sharpey.) 

 (Magnified about 150 diameters.) 



Three of the Haversian canals are seen, with their concentric rings ; also the lacunse, with 

 the canaliculi extending from them across the direction of the lamellee. The Haversian 

 apertures had become filled with air and debris in grinding down the section, and therefore 

 appear black in the figure, which represents the object as viewed with transmitted light. 



the included canal form what is known as a Haversian system. The 

 lacunae of a Haversian system communicate with one another and 

 with the Haversian canal, but not as a rule with the lacunae of other 

 Haversian systems. The angular interstices between the Haversian 

 systems are generally occupied by bony substance, which is fibrous but 

 not lamellar. Besides the lamellae of the Haversian systems there is a 

 certain thickness of bone at the surface, immediately underneath the 

 periosteum, which is composed of lamellae arranged parallel with the 

 surface ; these are the circumferential or periosteal lamellce (fig. 66, a). 

 They are pierced here and there by canals for blood-vessels, which are 

 proceeding from the periosteum to join the system of Haversian canals, 

 and also by calcified bundles of white fibres and by elastic fibres which 

 may also be prolonged from the periosteum. These are the perforating 

 fibres of Sharpey (fig. 68). 



The lamellae of bone are fibrous in structure. This may be seen in 

 shreds torn off from the superficial layers of a decalcified bone (fig 



