MAMMALIA. 311 



together with a very slight degree of flexibility. The general 

 form of a long bone is that of a shaft, having an enlarge- 

 ment at either extremity, the shaft is generally curved 



FIG. 75. LONG BONE (Femur). 



slightly so as to give elasticity, and is more solid than the 

 ends, which are expanded to give size and firmness to the 

 joints, and porous to keep them light ; the shaft is small 

 and close in its texture, that there may be plenty of room 



FIG. 76. SECTION OF BONE, MAGNIFIED. 



for the muscles which lie on and cover it. The skeleton 

 then, consists of bony cases which enclose the viscera, a 

 series of levers covered with, and moved by the muscles, 

 and the whole forming a solid framework to support the 

 soft parts. All the various motions of the body, from the 

 winking of the eyelid and the wonderfully adjusted motions 

 of the eye itself which are so accurate, that a certain per- 

 ceptible motion is required to look alternately at one side 



