STRUCTURE OF FOSSIL BONE. 77 



a piece be SKvra out just under the long incisor tooth ; the 

 piece from the rabbit will be found to be full of fine tubes 

 parallel with the tooth ; that of the hare with coarser and 

 more irregular ones ; in the rat few, and only the truncated 

 ends, will be seen ; and in the squirrel none at all."^ Do not 

 these variations accord with the habits and mode of life of 

 these different animals ; the rabbit and the hare can neither 

 gnaw a hole through wood, nor extract the kernel from a nut ; 

 but the rat can do the one in a masterly fashion, and the 

 squirrel the other. But I might multiply an infinity of 

 instances until I became tedious, and it is better that micro- 

 scopists should work them out for themselves. I merely 

 exhibit a few instances out of many fi*om which I have arrived 

 with certainty at the law that governs the texture and com- 

 position of bone, which may be thus briefly explained : 



That the Haversian tubes are connected with the move- 

 ments, habits, and mode of life of the liAang creature in which 

 they may be present. 



That the lacunae obey the same law, and adjust themselves 

 to the strains, pressure, and requisite density of any bone. 



That the canaliculi serve it also, and yet without any con- 

 fusion of the great classes of vertebrate animals. 



That all conspire in evincing the admirable unity of design, 

 and the harmonious correspondence of the bones with the 

 muscles, tendons, &c., of an organized being ; so that while 

 each living creature obeys the general law^ each maintains 

 also its distinctive characters. 



* Perhaps an odd one may appear, the cut requires to be carefully made, 

 as there are Haversian tubes on the side of the jaw, but different to those 

 of the rabbit. At the extreme edge there are round holes in the bone, 

 these are much more developed in the rabbit ; the course of the bone-cells 

 is irregular, mostly across, whereas they run longitudinally in the rabbit. 



