332 THE MECHANICAL FUNCTIONS, 



and compressed, approaching more or less to a 

 cubical shape. Of such is the colunni of the spine 

 composed, as also the joints of the wrist and ankle. 

 Where the principal object is either extensive pro- 

 tection, or the provision of broad surfaces for the 

 attachment of muscles, we find the osseous struc- 

 ture expanded into flat plates ; as is exemplified in 

 the bones of the skull, in the shoulder blade, and 

 still more remarkably in the bony shield which sur- 

 rounds the body of the tortoise. On the other 

 hand, where a system of levers is wanted, as in the 

 limbs, which have to sustain the weight of the 

 trunk, and to confer extensive powers of locomo- 

 tion, the bones are modelled into lengthened cylin- 

 ders, generally somewhat expanded at the extre- 

 mities, for greater convenience of mutual connexion. 

 In the form, the structure, and the arrangement 

 of these levers, which allow of the regular and 

 accurate application of the moving power, and are 

 calculated, in circumstances so various, to give 

 effectual support to the fabric, and also to execute 

 a great diversity of movements, we discern most 

 palpable manifestations of profound design, and 

 the most exquisite refinements of mechanic skill. 

 All the scientific principles of architecture and of 



number of minute opaque calcareous corpuscles, of an oblong shape, 

 and only about two or three times larger than the globules of the 

 blood. They are interspersed between the osseous fibres ; and are 

 arranged with some degree of regularity in rows surrounding the 

 canals of Havers, with the sides of which they are connected by very 

 slender filaments, radiating in every direction from the surface of the 

 corpuscles. Mr. Smee has found that these corpuscles are hollow, 

 and that their cavities occasionally communicate with those of the 

 canals. Proceedings of the Royal Society, Jan. 23, 1840. Miescher 

 considers the spongy substance in the interior of bones as being 

 formed by the canals of Havers, when much dilated. See Ann. 

 Sc. Nat. serie 2, xi. 33. 



