The Region of the Elbow. 67 



Hence, instead of being an euarthrodial or ball and socket 

 joint, the humero-radial is an arthrodial or gliding joint. 



The movements permitted at the elbow j.oint are : 

 Flexion and extension and, in addition, the gliding and 

 rotatory movements of the radius. Since the hand is at- 

 tached to the lower part of the radius, the radio-humeral 

 joint allows the radius, and, with it the hand, to be rotated, 

 i.e., supinated and pronated, and, because of the pecu- 

 liar relationship of the head of the radius to the humerus, 

 these movements of pronation and supination of the hand 

 may take place in any degree of flexion or extension of 

 the joint a wise provision, since it gives greater scope for 

 the performance of the delicate movements necessary for 

 the perfect action of the hand in the different occupations. 



Line of Joint. When the arm is partially flexed, 

 a transverse crease is noticed in front of the elbow with 

 its convexity downwards and its extremities touching 

 the condyles. The joint lies about half an inch below 

 this crease, and, since the inner margin of the articular 

 surface of the humerus is prolonged downwards, i.e., 

 toward the forearm, more than the outer margin is, and, 

 since the two condyles are onthe same level, it follows 

 that the line of joint is farther from the internal than it is 

 from the external condyle, i.e., the line of joint is one 

 inch below the internal condyle and three-quarters of an 

 inch below the external condyle. The articular surface of 

 the humerus is one and one-half inches wide and is divided 

 into two parts by an antero-posterior ridge, the inner and 

 larger part articulating with the ulna, while the smaller 

 and outer part articulates with the radius. When the arm 

 is by the side and the forearm is extended the vertical axes 

 of the arm and forearm are not in the same plane, but 

 meet at an angle of 20 (in the negro, 35). This is due 

 to the obliquity of that part of the articular surface that 



