AND PHYSIOLOGY. 



33 



That is, bone when used as a lever is 22 times as strong as 

 Sandstone, 3 \ times as strong as Lead, nearly 2| times as 

 strong as Elm and Ash, and 2 times as strong as Box, Yew, 

 and Oak timber. 



85. Microscopic Structure of Bone. Fig. si. 



Haversian Canals, — Examined by 

 the microscope the bones are found to 

 be made up of plates or layers for 

 the most part, arranged concentrically 

 in the long bones, and in parallel 

 layers in the flat ones. These are 

 traversed in all directions, and espe- 

 cially in their long diameters, by 

 minute tubes or vessels called Ha- 

 versian canals, which are also en- 

 circled by several lamina or plates 

 besides those following the general 

 outline of the bone. Fig. 31. These 

 canals have a diameter varying from 

 Woo to o loth of an inch, while the 

 accompanying lamellae show a thick- 

 ness of eoVoth of an inch. They 

 sometimes contain a capillary vessel, 



but more usually carry only the nutritive and watery portion 

 of the blood. 



8G. Lacuna, Canaliculi. — Besides these canals we find a 

 smaller set of vessels or cells located directly in the substance 

 of the concentric lamellae, called Lacunae or Bone Corpuscles, 

 which average T oVo th of an inch in length, and carry the fluid 

 which nourishes the bone. These are of a black appearance, 

 of an oval form, and with rays divergent in all directions, as 



Transverse section of bone 

 magnified 15 diameters. 1, Outer 

 layer. 2 and 3, inner layers. 



85. How are the particles of matter arranged in the long bones ? How in the flat 

 ones? Describe the Haversian canals. Their diameter. What vessel does each one 

 contain and what is the purpose of that vessel? 8G. What are the Lacunae or Bona 

 Corpuscles ? 



