STRUCTURE. 



85 



The laciinfe, 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 cavity. The lacunfe present some variety of 

 figure, but in such a section as that represented they for the most part 

 appear irregularly fusiform, and lie nearly in the same direction as the 

 lamella between which they are situated ; or, to speak more correctly, 



Pig. 49. — Transverse Section op Compact Tissue (of humerus) magnified about 



150 DIAMETERS. 



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

 or lacunre, with the canaliculi extending from them aci'oss the directiou of the lamellae. 

 The Haversian ajjertures had become filled with debris in grinding down the section, and 

 therefore appear black in the figure, which represents the object as viewed with trans- 

 mitted lisrht. 



the little cavities are flattened and extended conformably with the 

 lamellae ; for when the bone is cut longitudinally, their sections still 

 appear fusiform and lengthened out in the direction of the lamellae. 

 The canaliculi, on the other hand, pass across the lamella, and they 

 communicate with those proceeding from the next range of lacuna, so 

 as to connect the little cavities with each other ; and thus since the 

 canaliculi of the most central range open into the Haversian canal, a 

 system of continuous passages is established by these minute tubes and 

 their lacunas, along which fluids may be conducted from the Haversian 

 canal through its series of surrounding lamella? ; indeed, it seems 

 probable that the chief purpose of these minute passages is to allow 

 nutrient matter to be conveyed from the vascular Haversian canals 

 through the mass of hard bone which lies around and between them. 

 In like manner the canaliculi open into the great medullary canal, 

 and into the cavities of the cancellated texture ; for in the thin 

 bony parietes of these cavities lacunae are also contained ; they 

 exist, indeed, in all parts of the bony tissue. As first shown 



