STRUCTURE, ACTION, AND THOUGHT. 



761 



straight above him. If you go through these movements you will 

 find that your first impulse is to take a slight breath, which is 

 chiefly effected by the diaphragm, and on looking at the brachial 

 plexus you find that the first branch which is given off from the 

 fifth nerve is a filament to the phrenic (Fig. 13). Then, just as you 

 proceed to raise your shoulder, you take a still deeper breath, and 

 this, too, is represented in the plexus by the posterior thoracic 

 nerve, starting from the fifth and sixth nerves and going to the 

 serratus magnus, which has little power to raise the ribs and act 

 as an inspiratory muscle while the shoulder is depressed, but will 



Fig. 14. 



-Expulsion from Paradise. (After Raphael.) The position of Eve's right hand 

 shows the action of the seventh cervical nerve. 



do so when the arm is raised. If your hand is hanging by your 

 side, you will find the shoulder slightly drawn backward by the 

 rhomboid and the arm rotated a little outward by the infraspinatus, 

 which is supplied hy the suprascapular nerve. Next, you raise 

 your arm, and as you do so you will find that unconsciously you 

 bend it and turn it out, you extend the wrist and flex the fingers. 

 The raising of the arm and turning it out is effected by the deltoid 

 and teres minor, which are innervated by the circumflex nerve, 

 while the shoulder is still further raised by the trapezius, which gets 

 its nervous supply from a higher source — the spinal accessory. The 

 biceps and other flexors of the arm receive their supply through 



