progiiekSSio:^ on the land. 



53 



arranged, the screw in this instance being split up. At the 

 ankle the bones of the leg are applied to those of the foot by 

 spiral articular surfaces analogous to those found at the knee- 

 joint. The weight of the trunk is thus thrown on the foot, 

 not in straight lines, but in a series of curves. The foot 

 itself is wonderfully adapted to receive the pressure from 

 above. It consists of a series of small bones (the tarsal, 

 metatarsal, and phalangeal bones), arranged in the form of a 

 double arch ; the one arch extending from the heel towards 

 the toes, the other arch across the foot. The foot is so con- 

 trived that it is at once firm, elastic, and moveable, — -qualities 

 which enable it to sustain pressure . from above, and exert 

 pressure from beneath. In walking, the heel first reaches 

 and first leaves the ground. When the heel is elevated the 

 weight of the body falls more and more on the centre of 

 the foot and toes, the latter spreading out ^ as in birds, to 

 seize the ground and lever the trunk forward. It is in this 

 movement that the wonderful mechanism of the foot is dis- 

 played to most advantage, the multiplicity of joints in the 

 foot all yielding a little to confer that elasticity of step which 

 is so agreeable to behold, and which is one of the character- 

 istics of youth. The foot may be said to roll over the ground 

 in a direction from behind forwards. I have stated that the 

 angles formed by the bones of the human leg are larger than 

 those formed by the bones of the leg of the quadruped and bird. 

 This is especially true of the angle formed by the femur with 

 the ilium, which, because of the upward direction given to the 

 crest of the ilium in man, is so great that it virtually ceases 

 to be an angle. 



The bones of the superior extremities in man merit atten- 

 tion from the fact that in walking and running they oscillate 

 in opposite directions, and alternate and keep time with the 

 legs, which oscillate in a similar manner. The arms are arti- 

 culated at the shoulders by ball-and-socket joints to cup-shaped 

 depressions (glenoid cavities) closely resembling those found at 

 the hip-joints. The bone of the arm (humerus) is carried away 



1 The spreading action of the toes is seen to perfection in chihiren. It is 

 more or less destroyed in adults from a faulty principle in boot and slioemak- 

 ing, the soles being invariably too narrow. 



