50 



THE ESSENTIALS OF HISTOLOGY 



transmitted light, as do also the lacunas and canaliculi (fig. 59). Most 

 of the lamella? in compact bone are disposed concentrically around the 

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



FIG. 59. TiiAxsvEK-sE SECTION OF COMPACT TISSUE (OF HUMERUS). (Magnified 

 about 150 diameters.) 



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

 the cana'.iculi extending from them across the direction of the lamellae. 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 distinctly lamellar. Besides the lamellae of the Haversian systems 

 there is a certain thickness of bone at the surface, immediately under- 

 neath the periosteum, which is composed of lamellae arranged parallel 

 with the surface ; these are the circumferential or periosteal lamella 

 (fig. 58, 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. 60). 



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. 

 61). The fibres often cross one another in adjacent lamellae, and in 

 the Haversian systems they run in some lamellae concentrically, in 

 others parallel with the Haversian canal. In shreds of lamellae which 

 have been peeled off from the surface the perforating fibres may some- 

 times be seen projecting from the surface of the shred, having been 



