OF THE MOTORY APPARATUS IN MAN. 143 



scapula, and is moved by several powerful muscles, of which 

 some proceed from the scapula (sub-scapular, supra-spinal, 

 infra-spinal, teretes) ; others from the trunk, as the pectoralis 

 major, latissimus dorsi. By its lower or distal extremity, 

 it articulates with the radius and ulna. 



275. The radius and ulna form the skeleton of the 

 fore-arm. Of these, the radius is the more moveable, and 

 upon its rotation on the extremity of the humerus depends 



i Vertebral Column. Kibs. 



.--Clavicle. 



Intercostal! 

 Muscles. \ 



Fig. 96. Thorax of Man.* 



the movement of rotation and supination of the hand. There 

 is no rotation at the elbow-joint, both bones moving on the 

 humerus merely in flexion and extension ; but it is close to 

 this that the radius rotates on the ulna, and slides over the 

 smaller head of the humerus, which movement determines 

 the rotation of the hand in supination and pronation. The 

 lower end of the ulna is styliform, and has interposed between 

 * See explanation of this figure at page 77. 



