THE EXTREMITIES COMPARED 



373 



upper are organs of prehension, since they can reach forth and 

 secure various things which are required for the use of the body. 



Flexion of the arm is accomplished by a two-headed muscle 

 the biceps; flexion of the thigh by a double muscle, the ilio-psoas. 

 Extension of the elbow is accomplished by a three-headed muscle, 

 the triceps; extension of the knee requires a powerful four-headed 

 muscle, the quadriceps. 



We have learned to apply the terms medial and lateral to the 

 body while in the ana- 

 tomical position, in which 

 the forearm is supinated; 

 therefore the thumb is said 

 to be on the lateral border 

 of the hand, but the leg 

 cannot be supinated, and 

 the great toe lies on the 

 medial border of the foot 



Observe that the toes 

 of civilized man are freely 

 flexed and extended, but 

 have no other independent 

 motions. They are slightly 

 affected by the action of 

 plantar muscles, but the 

 foot has lost the suppleness 

 it might have had without 

 wearing shoes. The fin- 

 gers, however, can all be 

 moved sideways; the me- 



Ulnar nerve and artery 

 Radial nerve and 

 artery 



Branches to hand 



FIG. 240. THE FOREARM, ANTERIOR. 



dian line of the hand is a line drawn to the tip of the middle finger, 

 and the digits are said to be abducted or adducted, according as 

 their motion is from or toward this line. 



The freedom and mobility of the thumb add very greatly to the 

 usefulness of the hand in grasping, carrying, etc. If the fingertips 

 approach each other, the hand falls into a gently curved position 

 forming a cup, the "cup of Diogenes." If the hand be closed 

 forcibly with the thumb holding the fingers against the palm, it 

 becomes a solid irregular mass, the "fist," and so an ever-available 

 weapon of offense or defense. 



