258 



BONE OR OSSEOUS TISSUE. 



lamellae, but are mere channels piercing the periosteal lamellas. They are often spoken of as 

 Volkmann's canals. 



The cancellated texture has essentially the same lamellar structure. The slender 

 bony walls of its little cavities or areolse are made up of superimposed lamellae, like 

 those of the Haversian canals, only they have fewer lamellae in proportion to the 

 width of the cavities which they surround ; and, indeed, the relative amount of 

 solid matter and open space constitutes, as already said, the only difference between 

 the two forms of bony tissue : the intimate structure of the solid substance and the 

 manner of its disposition round the cavities being essentially the same in both. 



Lacunae and canaliculi. All over the section numerous little dark specks are 

 seen among the lamellae. These were named the " osseous corpuscles ; " but as it is 

 now known that they are in reality minute cavities existing in the bony substance, 

 the name of lacunce, has since been more fittingly applied to them. To see the lacunse 



Fig. 298. TRANSVERSE SECTION OF COMPACT TISSUE (OF HUMERUS). MAGNIFIED ABOUT 150 DIAMETERS 



(Sharpey). 



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

 canaliculi extending from them across the direction of the lamellae. The Haversian apertures had become 

 filled with air and debris (from the grinding), and therefore appear black in the figure, which represents 

 the object as viewed with transmitted light. 



properly, however, sections of unsoftened bones must be prepared and ground very 

 thin, and a magnifying power of from 200 to 300 must be employed. Such a 

 section, viewed with transmitted light, has the appearance represented in fig. 298. 

 The openings of the Haversian canals are seen with their encircling lamellae, and 

 among these the lacunae, which are mostly ranged in a corresponding order, appear 

 as black, opaque or nearly opaque oblong spots, with fine dark lines extend- 

 ing from them and causing them to look not unlike little black insects. The dark 

 appearance is due to the fact that the little cavities have become filled with air in 

 the dry bone, and when the same section is seen against a dark ground, with the 

 light falling on it (as we usually view an opaque object), the little bodies and lines 

 appear quite white, like figures drawn with chalk on a slate, and the intermediate 

 substance, being transparent, now appears dark. 



The lacunas, as already stated, are minute recesses in the bone, and the lines 

 extending from them are fine pores or tubes named canaliculi, which issue from their 



