82 STUDIES IN ADVANCED PHYSIOLOGY. 



ula is the bone of the forearm called the humerus. This 

 articulates at the elbow with two bones, the radius and the 

 ulna. The ulna forms the main articulation, forming really 

 the hinge joint of the elbow. The backward process on the 

 ulna, which prevents the backward flection of the elbow 

 joint, is called the olecranon process. This is really an 

 elbow cap, similar to the knee cap, which, however, in this 

 case has become firmly attached to the ulna. 



At the wrist the radius and ulna articulate with a series 

 of eight bones called the carpal bohes. Here the radius 

 forms the main articulation, and by rotating around the ulna 

 the hand is pronated and supinated. These carpal bones 

 are followed by five metacarpal bones, to which in turn are 

 connected three phalanges for each finger, the thumb hav- 

 ing but two. The radius is on the thumb side of the wrist. 



ISCHIUM 



Fig. 30. RIGHT os INNOMINATUM. 



Attached to the sacrum on each side is the os innom- 

 inatum, so called because the early anatomists were not 

 able to name it after any object they knew. This bone 



