75» 



THE POPULAR SCIENCE MONTHLY 



muscle rotates the body outward on the fixed thigh and thus 

 brings the center of gravity of the person over the resting foot. 

 If it were not for these muscles we should run a risk of falling 

 down as we lifted one leg instead of balancing ourselves with 

 comfort upon that one which is resting upon the ground. 



But we may now pass away from the muscles and nerves to 

 the nervous centers from which they receive their stimulus to ac- 

 tion, and whatever doubt may exist in regard to the adaptation of 

 the muscles to the peripheral nerves and the action of plucking 



and eating the apple, I 

 think there can be no 

 doubt at all that such 

 an arrangement exists in 

 the motor centers of the 

 brain. These centers were 

 localized in the monkey 

 by Ferrier, and it is the 

 difficulty I have had in 

 remembering their posi- 

 tion that has led me to 

 arrange them in accord- 

 ance with some definite 

 movements in a series of 

 actions to which I have 

 found they corresponded. 

 If we start from the posterior part of the second frontal con- 

 volution, pass upward along it and then across to the ascending 

 frontal convolution, follow this downward parallel to the fissure 

 of Rolando, and then turning the end of this fissure ascend again 

 upward along the parietal convolution which lies behind the fis- 

 sure, we find (Fig. 9) that the centers are arranged in the very 

 order required for looking at the apple, stretching out the hand 

 to take it, bringing it to the mouth, separating the seeds and throw- 

 ing them away. The aim and object of the whole series of ac- 

 tions is to eat the apple, and we find that the centers for doing 

 this are situated exactly where we should expect them — at the 

 very end of the fissure of Rolando. In Ferrier's description we 

 know that the movement which brings the hand to the mouth ap- 

 pears to be repeated on both sides of the fissure of Rolando, but it 

 appears that the part anterior to the former would bring the 

 hand to the mouth with the apple, while the part situated behind 

 the fissure of Rolando would throw the remnants of it away. 

 And here comes in a very interesting point : In order to complete 

 the series of actions necessary for Eve to go and get another 

 apple for Adam, you require movements of the leg (Fig. 10), and 

 these are not fully represented on the surface of the brain. But 





Fig. 11. — Diagram of Brain of Dog. (After Ferrier.) 

 C. S., Crucial sulcus. 1. Movements of eyes, as if to 

 see freely. 2 and 3. Movements of fore leg, and 4, 

 of hind leg, as in running. 5. Movements of tail 

 requisite in turning quickly, as when a greyhound is 

 following a hare when it doubles, x x x Move- 

 ments of mouth and jaws. 



