STRUCTURE OF BONE. 

 Fig. I.* 



and nerves, and in certain situations the lamellae separate from each 

 other, and leave between them areolar spaces (cancelli) of various 

 magnitude. The lamellae have an average diameter of ^W of an 

 inch, and besides constituting the general structure of the basis sub- 

 stance, are collected concentrically around the Haversian canals, and 

 form boundaries to those canals of about -^-Q of an inch in thickness. 

 The number of lamellae surrounding each Haversian canal, is commonly 

 ten or fifteen, and the diameters of the canals have a medium average 

 of ^^ of an inch. The cancelli of bone like its compact substance 

 have walls which are composed of lamellae, and such is the similarity 

 in structure of the parts of a bone, that the entire bone may be com- 

 pared to an Haversian canal of which the medullary cavity is the mag- 

 nified channel ; and the Haversian canals may be likened to elongated 

 and ramified cancelli. The Haversian canals are smallest near the 



1 Minute structure of hone, drawn with the miscroscope from nature, by 

 Bagg. Magnified 300 diameters. 1. One of the Haversian canals surrounded 

 by its concentric lamellae. The corpuscles are seen between the lamellae ; but 

 the calcigerous tubuli are omitted. 2. An Haversian canal with its concentric 

 lamellae, Purkinjean corpuscles, and tubuli. 3. The area of one of the canals. 

 4, 4. Direction of the lamellae of the great medullary canal. Between the 

 lamellae at the upper part of the figure, several very long corpuscles with 

 their tubuli are seen. In the lower part of the figure, the outlines of three 

 other canals are given, in order to show their form and mode of arrangement in 

 the entire bone. 



