BONE. 115 



The substance of bone presents numerous black, some- 

 what elongated bodies (fig. 15 a), called the lacuna 

 (lacuna, a little hollow) or bone-corpuscles, which are 

 however hollow, therefore not truly corpuscles, as 

 they were formerly considered. Between the adjacent 

 lacunae run numerous fine, dark, branched lines, con- 

 sisting of very minute canals, or canalic'uli. If the 

 section of bone be viewed by reflected light, the 

 lacunae and canaliculi will appear white. In the dried 

 bone they contain air. 



The structure of bone is best seen when viewed as 

 a transparent object in the dry state; for when the 

 section is immersed in liquid, the lacunae and canali- 

 culi become filled up. 



The size and form of the bone-corpuscles and canali- 

 culi vary in different animals, so much so that the 

 Class or Order to which an animal belongs may be 

 determined by reference to these particulars. 



Bone consists of earthy salts deposited in a finely 

 granular form throughout the substance of cartilage. 

 By soaking a piece of bone in vinegar or other dilute 

 acid, the earthy salts will be dissolved, the soft carti- 

 lage being left. But the structure of cartilage may be 

 best observed by making thin sections of the gristle 

 covering the ends of bones. It exhibits a bluish- 

 white basis (PL IX. fig. 16), in which are imbedded 

 numerous cells or cartilage-corpuscles, often under- 

 going cell-division. In some kinds of cartilage, the 

 basis is composed of fibres. 



Muscle. On examining a piece of the red flesh of 

 an animal under a low power, the mass will exhibit 

 a number of coarse, parallel, longitudinal, dark lines 

 (PL IX. fig. 20), the substance between these lines 

 being marked with cross or transverse striae, or lines, 

 and with fine longitudinal lines. The coarse longitu- 

 dinal lines indicate the intervals between bundles of 

 slender fibres, or fibril'lce, of which muscle consists. 

 The fibrillae (fig. 20 b, c) are very difficult to separate ; 



