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plane becomes a coronal plane when the arm hangs down along the side 

 of the body, and therefore I still call it the coronal plane. In the same 

 position the perpendicular plane is parallel with the sagittal plane of 

 the body and may therefore be called the sagittal plane of the arm. The 

 intersection of the two planes forms the axis of the humerus passing 

 through the center of the upper third of the shaft and through the axis 

 of the elbow below the coronoid process. 



Diagram of the bones of the arm with the planes from which measurements 

 were taken indicated. D, circle of maximum deflection of the ulna; d chord 

 of the arc of deflection when the elbow is extended: d', the same at about 110 

 degrees; e, chord of the arc of extension when reduced to degrees to be sub- 

 tracted from 180 degrees; f, chord by which the extent of the flexion of the 

 elbow is measured. 



The angle of the axis of the joint with the long axis of the humerus 

 was first determined by direct measurement, the right arm being clamped 

 with the humerus to my left, and the left arm in the opposite position. 

 In all cases the degree of flexion, extension and deflection was deter- 

 mined by measuring from the styloid process of the ulna. The degree 



