THE SKELETON. 



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osseous : the exo- and splanclino-skeletons may offer also another, 

 or fourth condition, viz. the albuminous, or epidermal. 



The most common tissue of the endo-skeleton of the Vertebrata is 

 that called " bone," and it is peculiar to this primary division of the 

 Animal Kingdom. 



Bone consists of animal, chiefly gelatinous, matter, hardened by a 

 general but regulated diffusion of earthy molecules ; the proportion 

 of organic to inorganic matter varies in different classes. Fishes 

 have the least, Birds the largest proportion of earthy matter ; and of 

 the two, in this respect, intermediate classes, the Mammalia, espe- 

 cially the active predatory species, have more earth, or harder bones, 

 than Reptiles. This difference depends chiefly uj^on the quantity of 

 fluid, or evaporable matter, in the cells and tubes of the animal basis, 

 but not wholly, as some have supposed ; at least the apparently 

 exact, cei'tainly most carefully and scientifically conducted experi- 

 ments of M. Bibra (iv.) on thoroughly dried portions of bone, show 

 the following differences : — 



PROPORTIONS OF EARTHY AND ANIMAL MATTER IN THE BONES OP 

 VERTEBRATE AJ^IIMALS. 



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