THE ERECT POSITION IN MAN. 229 



the axis of the spinal column is due to the vertical direction of 

 the shaft of the iliac bone, along with the complete extension 

 of the hip-joint. 



7.— The Leg. 



a. In no animal are the tibia and fibula collectively so 

 fully developed and adapted to the actions of the foot, as in 

 man. 



b. In no animal can the leg be extended into the line of 

 axis of the thigh. 



c. The human knee-joint is the only knee-joint which ad- 

 mits of complete extension. 



d. It is the only knee-joint provided with a complete 

 extensor area. 



e. No form of leg presents extensor muscles so powerful 

 as the human. 



/. The massive flexor muscles of the human leg act mainly 

 on the trunk. 



8.— The Foot. 



a. The human foot is a plantigrade foot. 



6. The plantigrade foot in the animal is so constituted 

 that its five digital columns (axes) are more or less uniformly 

 engaged in the actions of the foot itself. In the human foot, 

 again, its four outer digital columns play a subordinate part, 

 while the inner column, that of the hallux, becomes the axis 

 of the foot itself. 



c. The four outer or subordinate columns of the human 

 fool are arranged in two groups — the second and third forming 

 the inner group next the hallux ; the fourth and tilth the 

 outer group. 



(I. The human foot has, moreover, its constituent bones 

 arranged in two longitudinal series, or compound columns. 

 The outer column, cominciicin.'j, U hind, below, and externally 

 at the heel in the calcaneum, terminates in front and e\ter- 



