28 



ELEMENTARY PHYSIOLOGY 



humerus, forming the olecranon process (Gr. olene, the elbow ; and 

 kranion, the top) or prominence of the elbow, which gives attach- 

 ment to certain muscles, and prevents the forearm from moving 

 too far back. The radius is slender at the top, where its shallow 

 cup-like end articulates with a convex surface furnished by the 

 humerus. Its lower extremity is enlarged, and gives attachment 

 to the bones of the wrist. If we rest the forearm flat on a table, 

 with the palm of the hand uppermost (an attitude which is called 

 supination), the ulna and the radius are parallel with each other. 



If we now turn the hand round till its 

 back is uppermost (pronatiori) the 

 ulna does not change its position; 

 but the lower end of the radius 

 turns round this bone, crossing it, 

 and carrying the hand with it. Thus 

 the upper slender end of the radius 

 rotates on a pivot formed by a 

 rounded portion of the lower head 

 of the humerus, and is held in its 

 position by a circular ligament, while 

 its lower extremity revolves round 

 the ulna. 



The wrist is composed of eight 

 small bones, called carpal bones 

 (Gr. karpos, the wrist), arranged in 

 two rows of four. These bones are 

 united with one another and with 

 the neighbouring bones by means 

 of ligaments, in such a manner that 

 each one is capable of a slight 

 gliding motion. The wrist is thus 

 rendered flexible ; and this flexi- 

 bility, combined with the rotatory 

 motion of the radius, gives great freedom of movement to the hand. 

 Five long bones, called metacarpal bones (Gr. vieta, beyond ; 

 and karpos, the wrist), form the palm of the hand. One of these 

 passes from the wrist to the thumb, and the other four from the 

 wrist to the ringers. These bones may be easily felt by pressing 

 the fingers of one hand over the back of the other. It will, of 

 course, be observed that the metacarpal bone which is connected 

 with the thumb is capable of motion to a far greater degree than 

 the others. It is on this that the utility of the thumb depends, 

 for we are enabled to move the thumb round till it is in opposition 

 to the fingers, and thus to firmly grasp large objects and to pick 

 up small ones. 



Fig. 31. The Eight Hand from 

 before. 



c, carpal bones ; M, metacarpal bones ; 

 i, 2, and 3, phalanges. 



