300 THE SOLIDS. 



tween the osseous laminae already described, and by which 

 they are compressed ; they thus present in all sections of 

 bone an elongated or flattened form, and in transverse cut- 

 tings those facing the Haversian canals appear not merely 

 elongated, but also slightly curved, the concavity of the arc 

 being directed inwards towards the canals, and the convexity 

 outwards in the contrary direction. (See Plate XXXII. 



figs, i, 2.) 



When viewed as transparent objects they appear black, 

 and when as opaque they are of a pearly whiteness. 



From the margins of each bone cell proceed a number of 

 branched canals, which, passing through the lamellae situated 

 on either side of the cell, inosculate freely with the canaliculi 

 given off by the bone cells of the contiguous lamellae (see 

 Plate XXXII. fig. 3.) ; this process of inosculation being 

 frequently repeated between the cells of each lamella, a com- 

 munication is thus established between the medullary cavity 

 on which the canaliculi of the first series of cells opens, the 

 Haversian canals, and the external surface of the bone. The 

 reality of this communication may be attested by applying a 

 drop of oil of turpentine to a section of dry bone placed be- 

 neath the microscope, when the passage of the fluid through 

 the bone cells may be followed with the eye. This experi- 

 ment was first suggested by Drs. Todd and Bowman. 



The canaliculi of bone cells treated with acid usually dis- 

 appear, the body of the cell alone remaining. 



The size of the bone cell throughout the whole of osseous 

 vertebrate series, stands in relation to that of the red blood 

 disc; and Mr. Quekett, who has instituted an inquiry into their 

 form and size in a great variety of animals, has arrived at the 

 conclusion that the class to which any animal belongs, whe- 

 ther that of Beasts, Birds, Reptiles, or Fishes, may be deter- 

 mined by the two particulars referred to. This discovery is 

 likely to be especially useful in the determination of the true 

 position in the animal series of many fossil bones, which but 

 for.it would have continued to be enveloped in uncertainty 

 and conjecture. 



In many osseous fishes the bone cells appear to be wanting, 



