DEVELOPMENT OF BONE. 



45 



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

 compared to anHaversian 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 surface 

 of a bone, and largest near its centre, where they gradually merge into 

 cancelli ; by the frequent communications of their branches they form a 

 coarse network in the basis substance. 



Fig. 12 * 



The cells of bone, or corpuscles of Purkinje, are thickly disseminateil 

 through the basis substance ; they are irregular in size and form, give 

 off numerous minute branching tubuli, which radiate from all parts of 

 their circumference, and in the dried state of the bone contain merely 

 the remains of membranous cells and some calcareous salts. f In the 

 living bone, the cells and their tubuli are probably filled with a nutritive 

 fluid holding calcareous salts in solution. The form of the cells is oval 

 or round, and more or less flattened, their long diameter corresponds 

 with the long axis of the bone, and their tubuli cross the direction of the 

 lamellae, and constitute a very delicate network in the basis substance, 

 by communicating with each other, and with the tubuli of neighbouring 

 cells. The tubuli of the cells nearest the Haversian canals terminate 

 upon the internal surface of those cavities. The size of the cells varies 

 in extreme measurement from 5^00 to gj^ of an inch in their long diame- 

 ter, an ordinary average being y^ou ; the breadth of the oval cells is 

 about one-half or one-third their length, and their thickness one-half 

 their breadth. They are situated between the lamella, to which circum- 

 stance they owe their compressed form. 



* The above cut, which I have introduced to supply the manifest deficiency of Mr. 

 Wilson's representation, is from a section of a human femur, about its middle, and ex- 

 hibits the erratic course of the Haversian canals, and their relations to each other, and 

 at the same time the general laminated condition of a long bone. This laminated con- 

 dition is well shown by polarized light, which causes the corpuscles to disappear, and 

 the laminae to come out boldly. G. 



j-Miiller and Henle conceived that the bone cells and tubuli were the principal sea : 

 of the calcareous matter. Hence they have been named calcigerous cells and tubuli. 



