MANIPULATION. THE ARM AND HAND. 195 



notch (smaller sigmoid) on the outer side of the ulna, and a strong 

 collar-like ligament, named orbicular, 4, passes from both borders of 

 this sigmoid notch, and embraces the head of the radius, without being 

 fixed to it. Hence, although, at the elbow-joint, the radius is carried 

 to and fro with the ulna, upon the humerus, in the movements of flexion 

 and extension of the forearm upon the arm, yet, provision is made in 

 the mode of articulation of the radius and ulna at their upper ends, 

 for that peculiar motion between the two bones, which constitutes pro- 

 nation and supination of the forearm and hand. 



A line drawn through the elbow-joint, from side to side, is oblique, 

 the inner condyle of the humerus being longer than the outer one ; in 

 consequence of this, when the joint is flexed, the forearm is not bent 

 directly upon the arm, but is carried to its inner side, that is, a little 

 over the body; a similar inclination inwards of the hand, when it bends 

 at the wrist, carries it also still further in front of the body, and hence 

 the hand is brought, by the mere mechanism of the articular surfaces, 

 into a position of constant utility and advantage. At its lower end, 

 the radius is widened out, Fig. 54, 7, and rolls upon the ulna, the two 

 bones being tied together by a strong fibro-cartilage, S, which passes 

 from the inner border of the radius and neighboring ligaments, below 

 the articular end of the ulna, to be attached to the styloid process of 

 that bone; a small notch on the side of the radius receives a rounded 

 part of the ulna, the reverse arrangement to that which takes place 

 at the upper ends of the bones, where the radius is received into the 

 ulna. The hand is principally connected with the lower end of the 

 radius, the lower articular surface of the ulna being excluded by the 

 fibro-cartilage just mentioned; hence, the hand moves with the radius, 

 and when that bone is rolled upon its axis, supported on the ulna, the 

 hand moves with it, the rolling motion inwards, in which the palm of 

 the hand is turned downwards, being called pronation, from the word 

 prone (lying on the face) ; whilst the rolling motion outwards, in which 

 the palm of the hand is turned upwards and its back downwards, is 

 called supination, from supine (lying on the back). 



This most admirable arrangement multiplies the use of the hand, 

 enabling it, by this simple additional movement, to operate upwards 

 or downwards, or at any intermediate point. The general motion at 

 the wrist-joint is of a hinge-like character, but slight lateral move- 

 ments increase the flexibility of the joint in those directions, and this 

 is also augmented, in the direction of flexion, by the arrangement of 

 the carpal bones into two rows. The hand itself is slightly arched 

 transversely in the palm, like the foot in the sole, but scarcely so from 

 before backwards; the concavity of the palm is not intended to give 

 it strength as an organ of support, but besides affording protection to 

 important bloodvessels and nerves, it serves to adapt the hand for hold- 

 ing purposes; moreover, the ends of the metacarpal bones on which 

 the fingers are supported, when looked at endways, are seen to form 

 a curved line, in consequence of which the fingers, when closed, are 

 thrown together, pointing towards the middle of the palm, and are 

 more easily opposed to the thumb. The joints at the base of the 

 fingers, being ball and socket joints, those digits may be spread out 



