THE HUMAN HAND ; A SCHOOL LESSON 37 



it would be if wherever the wrist or a .finger- joint was 

 bent, a tendon stretched across the angle, taking the 

 shortest course between its two points of attachment ! 



We have noticed the two flexor tendons which can be 

 seen through the skin on the front of the wrist. One of 

 these, that nearest to the thumb, is a convenient guide 

 to the pulse. A good-sized artery, the radial artery, here 

 runs just beneath the skin, on the thumb side of the 

 tendon. By pressing the finger-ends upon the radial 

 artery the pulse is felt. 



The usefulness of the human hand is greatly promoted 

 by the power of turning it round. Hold your hand palm 

 upwards and thumb outwards. Then turn it over, so 

 that the palm looks downwards, and the thumb turns 

 inwards. There are few animals which can perform that 

 simple action. Those which can do so are nearly all 

 climbing animals, which use the hand, and perhaps the 

 foot also, to grasp with, and may require to turn the hand 

 in all sorts of positions in order to get hold of a bough in 

 the most convenient way. Observe that you cannot turn 

 your hand over except by swinging the thumb round the 

 little finger. Lay your hand on the table and perform 

 this action once or twice. Then try to swing the little 

 finger round the thumb, keeping the thumb pressed against 

 the table. The action can only be imperfectly executed, 

 and then by bending both elbow and wrist into a very 

 awkward position. This shows us that the hand is not 

 merely rotated on a pivot or a pin ; such an arrangement 

 as that would be quite impossible. 



There are two long bones in the human forearm, the 

 radius and the ulna. It is the radius chiefly which carries 

 the hand and forms the wrist- joint ; it is the ulna chiefly 

 which enters into the elbow- joint. You can make a 

 model of the arrangement with two long pencils, a cork, 

 and an indiarubber band. Lay the pencils side by side, 

 with the cork lying between two of their ends, and bind 

 pencils and cork together by the indiarubber band. Cut 



