LESSON VII. 



BONE, OSSIFICATION, TEETH. 



A. STRUCTURE OF BONE. 



1. Examine under a low power prepared transverse 

 sections 1 through the shaft of a long bone. 

 Most of the smaller spaces (i.e. Haversian canals, 

 lacunae, canaliculi) will be filled with air or 

 debris and will therefore appear dark. Observe 



a. The central cavity surrounded by a small 

 amount of spongy bone which is arranged in 

 a network with rather large irregular spaces 

 (Haversian spaces) ; externally the spongy 

 bone passes into the compact bone : note the 

 transition from the Haversian spaces to the 

 Haversian canals. 



b. In the compact bone the Haversian systems, 

 each consisting of a Haversian canal sur- 

 rounded by concentric lamellae which are 

 chiefly marked off from one another by the 

 lacunae which lie between them. 



1 It is simplest to buy these sections. 



