762 THE POPULAR SCIENCE MONTHLY. 



the musculocutaneous nerve from the outer cord. In the move- 

 ments of the wrist and fingers the fifth and sixth nerves appear 

 to co-operate, and those of the fingers are chiefly due to the sixth. 

 The supinators and extensors of the wrist, fingers, and thumb get 

 their nerves from the musculo-spiral or its interosseous branch. 

 To resume, the fifth and sixth cervical nerves raise the shoulder, 

 flex the forearm, and extend the wrist. The nervous energy passes 

 from them along the upper trunk and outer cord of the brachial 

 plexus to the flexors of the forearm, while the impulses to raise the 

 shoulder, rotate the humerus, and extend the wrist and fingers 

 travel chiefly through the posterior cord by the musculo-spiral 

 nerve and its interosseous branch to the extensors of the wrist 

 and digits. From the fifth and sixth cervical nerves we make a 

 jump to the first dorsal, which has an exactly opposite action. 

 The movements it produces are that the hand closes firmly upon 

 the apple, the wrist is twisted round into the prone position and 

 flexed to the ulnar side. The forearm is extended, and the upper 

 arm is retracted in the manner required to pull the apple from 

 the tree. In these movements, if you put your hand upon your 

 chest, you will find that the pectoral muscles are largely engaged, 

 and they receive their nerves partly from the internal cord of the 

 brachial plexus. Flexion to the ulnar side is produced by the 

 ulnar nerve, and the dragging of the arm down is effected by the 

 subscapular, teres major, and latissimus dorsi muscles, which are 

 supplied by the subscapular nerves, and the triceps by which the 

 arm is extended gets its nerve supply from the musculo-spiral. 

 But these movements, especially if executed forcibly, as they 

 would be if the apple were firmly attached, would bring the hand 

 below the level of the mouth, and the prone position would keep 

 the apple away. 



We must now go back to the sixth cervical nerve, which we 

 find will rectify this action, for it raises the arm inward and up- 

 ward with the forearm flexed, so as to bring the hand to the mouth, 

 supinated, and with the wrist and basal phalanges extended, so 

 as to present the apple comfortably for eating. In effecting this 

 movement the nervous impulses travel by the posterior thoracic, 

 circumflex, musculo-cutaneous, musculo-spiral, and median nerves 

 to the serratus magnus, deltoid, biceps, brachialis anticus, supina- 

 tor longus, and extensors of the wrist and basal phalanges. The 

 position of Adam's left hand in Raphael's picture shows this 

 action in its middle stage, before it has carried the hand to the 

 mouth. The few last phalanges of his fingers are flexed, and we 

 may suppose that the flexion is effected by means of the median 

 nerve, but it is just possible that their flexion may be due to me- 

 chanical pulling on the tendons by the extension of the wrist and 

 basal phalanges just as the hand is opened in the well-known 



