54 THE HUMAN BODY. 



are called lacunae; from each lacuna radiate many ex- 

 tremely fine tubes, the canaliculi^ so that each lacuna with 

 its canaliculi looks something like a small animal with a 

 great many legs. The innermost canaliculi open into the 

 Haversian canal of the system to which they belong, and 

 those of various lacunse communicate with one another, so 

 that a set of passages is provided through which liquid 

 which transudes from the blood-vessel in the Haversian 

 canal can ooze all through the bone. 



In a living bone a nucleated cell lies in each lacuna. 

 These cells, the bone corpuscles, are the remnants of those 

 which made the bone, all whose hard parts are but in- 

 tercellular substance: a sort of skeleton is made by each 

 cell around itself, and this adheres to the skeletons of the 

 rest, and thus the whole bone is built. 



Chemical composition of bone. Apart from the bone 

 corpuscles and the soft contents of the Haversian canals 

 and of the spaces of the cancellated bone, the hard bony 

 substance proper is composed of animal and mineral mat- 

 ters so intimately combined that the smallest distinguish- 

 able bit of bone contains both. The mineral matters give 

 the bone its hardness and stiffness, and form about two- 

 thirds of its weight when dried. They may be removed 

 by soaking the bone in diluted muriatic acid,* and the 



What radiate from the lacunae? Into what do the innermost 

 canaliculi of an Haversian system open? How is nourishing liquid 

 from the blood carried throughout a bone ? 



What lies in each lacuna of a living bone? What are the bone 

 corpuscles? What is the hard part of bone? How is a whole bone 

 made up ? 



Of what primary constituents is bone composed ? Is there any 

 fragment of bone that does not contain both ? What qualities do its 

 mineral parts give to a bone? How much of a dry bone consists of 

 mineral matter ? How may the mineral parts be removed ? 



* Add a couple of ounces of muriatic acid to a pint of water and place a 



