98 THE MICROSCOPIST. 



does not occur in all the cells, as the bone requires to grow 

 and be nourished; hence arises its peculiarity of structure. 

 Independently of its hollows, or cancelli, the hard part of 

 the bone is traversed by canals, called Haversian, which run 

 in the direction of the laminae ; these are connected by trans- 

 verse communications. In a thin transverse section of bone, 

 the solid matter may be observed arranged around the Haver- 

 sian canals in concentric rows (Fig. 29). Among these layers 

 dark specks are dispersed. These dark specks (called lacunse, 

 or corpuscles of Parkinje), when magnified about 200 diameters, 

 are observed to be cavities of an irregular, oval form, from 

 which emanate numerous minute branch canals. These cavi- 

 ties appear dark for the same reason as a minute air-bubble 

 does in Canada balsam, namely, the difference of refraction 

 of the two media. By means of these branches (canaliculi), 

 lacunae, and Haversian canals, the bone is nourished with 

 proper fluids. 



It has been shown by Mr. J. Quekett, that there are diffe- 

 rences in the form and size of the lacunae, in the various classes 

 of animals, sufficiently characteristic to allow of the assignment 

 of minute fragments of bone, with the aid of the microscope, 

 to their proper class. The lacunae of reptiles are distinguish- 

 able by their large size, and long oval form ; and those of fish, 

 by their angular form and the fewness of their radiating cana- 

 liculi. The lacunae of the bird may be distinguished from 

 those of the mammal, partly by their smaller size, but chiefly 

 by the remarkable tortuosity of their canaliculi. It is worthy 

 of remark, also, that the sizes of the lacunae in the four classes 

 of vertebrata, bear a close relation to the sizes of their blood- 

 corpuscles. 



SECTIONS or TEETH may be made in the same way as bone. 

 Some should be soaked in hydrochloric acid, to destroy the 

 earthy matter, and others in caustic potash, to get rid of animal 



