An academic physiology and hygiene .. . unded by powerful muscleswhich use it as a lever. EXPLANATION. All the bones of the arm, fore-arm,and hand, are here exhibited in con-nection, with reference to impressingit on the mind, after having read ashort description of the individual partsof the upper extremity. a is the head of the arm-bone, artic-ulated to the shoulder. b, the joint, or elbow, formed by theulna and lower end of the arm. c, the shaft of the os humeri, or arm. d, the radius, or handle of the hand,united solely to the wrist. g, the ulna, which alone forms withthe arm the joint. 21
An academic physiology and hygiene .. . unded by powerful muscleswhich use it as a lever. EXPLANATION. All the bones of the arm, fore-arm,and hand, are here exhibited in con-nection, with reference to impressingit on the mind, after having read ashort description of the individual partsof the upper extremity. a is the head of the arm-bone, artic-ulated to the shoulder. b, the joint, or elbow, formed by theulna and lower end of the arm. c, the shaft of the os humeri, or arm. d, the radius, or handle of the hand,united solely to the wrist. g, the ulna, which alone forms withthe arm the joint. 21. The fore-arm hastwo bones, the ulna(Lat., the elbow) andthe radius (Lat., a rayor a spoke), which ex- F9 9 tend from the elbow to the wrist. In addition to enter-ing into the formation of the elbow-joint, they jointhe carpal bones to form the wrist-joint, and with eachother at both extremities in such a way as to admit ofthe rotary motion of the hand. The ulna (the bone onthe little-finger side of the arm) enters principally with the. 28 ACADEMIC PHYSIOLOGY. humerus in forming the elbow-joint, as the radius doesnot touch the humerus till the fore-arm is drawn up to thearm. The radius, however, is so expanded as to enterprincipally into the formation of the wrist-joint. In therotary motion of the hand, the radius twists or glides overthe ulna when the palm is turned upward or downward,and when the thumb is uppermost the bones are parallel.
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