110 PHILOSOPHY OF ZOOLOGY 



to age, the earthy matter being smallest in youth, but, like- 

 wise, according to the nature of the bone itself, and the 

 purposes which it is destined to serve. The teeth contain 

 the largest portion of earthy matter. Remarkable diffe- 

 rences are likewise observable, according to the class or spe- 

 cies. The lx>nes of quadrupeds and birds contain a much 

 greater proportion of earthy matter than those of reptiles or 

 fishes. In some fishes, the earthy matter is so small, that 

 the cartilage continues, during the whole life of the ani- 

 mal, soft, flexible, and elastic, as the spine of the lamprey, 

 or a little more indurated, as in the bones of the skate and 

 shark. These fishes have been termed cartilaginous. 

 Even in those fishes which arc termed osseous, the cartilage 

 bears a much greater proportion to the earthy matter than 

 in quadrupeds. 



Bone is readily reproduced, in small quantities, especial- 

 ly in youth. In the case of fracture, the periosteum in- 

 flames and swells, the crevice is filled up by a cartilaginous 

 basis, abounding in vessels, and the earthy matter is at 

 length deposited, giving to the fractured part, in many 

 cases, a greater degree of strength than it originally pos- 

 sessed. 



In animals of the deer kind, the horns, which are true 

 bone, are annually cast off; a natural joint forming at their 

 base, between them and the bones of the cranium, with 

 which they are connected. They are afterwards reproduced 

 under a skin or periosteum, which the animal rubs off when 

 the new horns have attained their proper size. 



In some cases of disease, the earthy matter is again ab- 

 sorbed into the system, the cartilaginous basis predomi- 

 nates, and the bones become soft and tender. This takes 

 place in the disease of youth, termed Rickets, and in a si- 

 milar complaint of advanced life, known under the name of 

 Mfottities osftinm. In other instances, bone is formed as a 



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