BONES AND JOINTS OF THE EXTREMITIES 59 



f erent arches forward ; across ; and horizon- 

 tally : they are wedged together, and bound by 

 ligaments, and this is what we alluded to when 

 we said that the foundations of the Eddystone 

 were not laid on a better principle ; but our ad- 

 miration is more excited in observing, that the 

 bones of the foot are not only wedged together, 

 like the courses of stone for resistance, but that 

 solidity is combined with elasticity and lightness. 



Notwithstanding the mobility of the foot in 

 some positions, yet when the weight of the body 

 bears directly over it, it becomes immovable, and 

 the bones of the leg must be fractured before the 

 foot yields. 



We shall proceed to explain how the knee- 

 joint and hip- joint, independently of the exertion 

 of muscles, become firm in the standing position, 

 and when at rest : but, before we enter upon this, 

 let us understand the much-talked-of demonstra- 

 tion of Borelli, who explained the manner in 

 which a bird sits upon a branch when asleep : 

 the weight of the creature and the consequent 

 flexion of the limbs drawing the tendons of the 

 talons, so as to make them grasp the branch with- 

 out muscular effort. 



The muscle A passes over the joint at B, and 

 then proceeds to the back of the leg, and be- 

 hind the joint at C, and so descends behind the 

 foot at D, and extends to the talons; and the 



