STRUCTURE OF BONE. 371 



worthy of admiration, as evincing the skill with 

 which every part is adapted to its destined uses. 

 The animal membrane, which, as we have seen, 

 is the bed in which the calcareous phosphate is 

 deposited, partakes of the reticular structure 

 belonging to the ordinary cellular texture ; and 

 a bone, when minutely examined, exhibits also 

 the same appearance of plates intermixed with 

 fibres. In the outer compact portion, indeed, 

 the fibrous arrangement of the particles is not so 

 easily distinguished : but it may be detected in 

 young bones while they are becoming ossified : 

 and also in bones that have been long exposed 

 to the weather, or long macerated in water. The 

 interior of most bones, in the higher classes of 

 animals, presents distinctly the appearance of 

 irregular cavities, resulting from the partial sepa- 

 ration of the plates, and their mutual crossings, 

 and fibrous connexions. 



The different mechanical purposes for which 

 bones are employed in the animal economy 

 require them to be of different forms. Where 

 a part is intended to have compactness and 

 strength, with a very limited degree of motion, 

 it is divided into a great number of small pieces, 

 united together by ligaments, and the separate 

 bones are short and compressed, approaching 

 more or less to a cubical shape. Of such is the 

 column of the spine composed, as also the joints 

 of the wrist and ankle. Where the principal 



