212 THE ANIMAL KINGDOM. 



is a small web saw, a good hone, and patience. Slice a 

 thin bit of bone with the saw, and rub it on the hone with 

 water until transparent. Towards the end of the operation 

 fasten the section with balsam to a glass slide, and finish 

 the grinding carefully, when it may be dried and mounted 

 like any other object. 



The whole jaw of a Mole well ground down is very beau- 

 tiful, showing the Haversian tubes like a tree branching 

 out between the fangs of the molar teeth. 



Longitudinal sections generally show the structure best. 



In the position and use of a bone, the size and number 

 of the lacunae and Haversian canals are modified to give 

 the required strength or lightness. The wing-bones of 

 Birds abound in Haversian canals and lacunae, which give 

 both elasticity and strength, and there is an interesting 

 paper on this subject by the Rev. J. B. Dennis, in the 

 'Microscopical Journal' for 1843. For the guidance of 

 the student who may wish to collect specimens and prepare 

 sections of bone, the following table of the relative size of 

 bone-cells in Pishes, Reptiles, Birds, and Man, will be 

 useful : 



Measurement of lone-cells in parts of an English inch. 

 (TRANSVERSE SECTIONS.) 



L one of the smallest -^-oV 



