98 



THE HUMAN BODY. 



the tliumb outwards, the lower end of the radius can b& 

 felt on the outer side of the forearm just above the wrist, 

 and if this be done while the hand is turned over, it will 

 be easily discerned that during the movement this end of 

 the radius, carrying the hand with it, travels around the 

 lower end of the ulna so as to get to its inner side. The 

 relative position of the bones when the palm is upwards 

 is shown at A in Fig. 41, and when the palm is down at 

 B. The former position is known as supination; the lat- 

 ter as pronation. The elbow 

 end of the humerus (Fig. 36*) 

 bears a large articular surface: 

 on the inner two thirds of this, 

 Tr, the ulna fits, and the ridges 

 and grooves of both bones inter- 

 locking form a hinge-joint, al- 

 lowing only of bending or 

 straightening the forearm on 

 the arm. The radius fits on 

 the rounded outer third, Cpl, 

 and forms there a ball-and-socket 

 joint at which the movement 

 takes place when the hand is 

 turned from the supine to the 

 prone position; the ulna forming 

 a fixed bar around which the 

 lower end of the radius is moved. 

 Gliding Joints. These per- 

 mit as a rule but little move- 

 ment: examples are found be- 

 tween the closely packed bones of the tarsus (Fig. 35 f) and 

 carpus, which slide a little over one another when subjected 

 to pressure. 



Hygiene of the Joints. When a bone is displaced or 

 dislocated the ligaments around the joint are more or less 

 torn and other soft parts injured. This soon leads to in- 

 flammation and swelling which make not only the recogni- 

 tion of the injury but, after diagnosis, the replacement. 

 of the bone, or the reduction of the dislocation, difficult. 



FIG. 41. A, arm in supination 

 B, arm in pronation; if, humerus 

 B, radius; U, ulna. 



* P. 87. 



f P. 83. 



