LECTURE III. 141 



I must not dwell upon the form of the 

 bones or the structure of the joints in these 

 pelvic or lower extremities, lest I should 

 set my audience asleep. Suffice it then to 

 say, that when the knee-joint is extended, 

 so that the leg makes a perpendicular line 

 with the thigh, and the ankle bent, so that 

 the foot forms a right angle with the leg, 

 each of these joints is rigid and immove- 

 able. Such is their position when we 

 stand ; the whole limb forming a pillar for 

 our support, and no motion can take place 

 but at the top or bottom, at the hip or 

 foot. But when the knee is bent, and the 

 foot stretched out, as happens in progres- 

 sion, the same joints are loosened, and a 

 lateral motion admitted, which is useful in 

 the direction of our steps. The knee is 

 secured in its extended state, so necessary 

 for our support, by muscles which are in- 

 comparably the strongest in the whole 

 body ; and which hold the knee-pan ele- 

 vated to the top of a pully formed in the 

 front of the joint. But when these muscles 

 are weak, then indeed are " the pregnant 

 hinges of the knee disposed to crook," and 



