272 THE HUMAN MECHANISM 



The spinal cord alone, then, and without the help of the 

 brain, is capable of maintaining a small part of the normal 

 posture of the resting frog and also of executing some of 

 the simple reflexes, especially those involving movements 

 of the hind legs, but it does not seem to be capable of 

 originating actions or of doing any except reflex actions. 



6. The behavior of a frog with spinal cord and bulb only. 

 In this case there is no new feature in the maintenance of 

 posture ; the frog lies on its belly and executes the same 

 reflexes as before. The respiratory movements, however, go 

 on in a normal manner; the vasomotor tone of the arteries 

 is maintained, most vasomotor reflexes may be produced 

 with ease, and the heart may be reflexly inhibited. As com- 

 pared with the brainless frog, the number of actions which 

 the animal can execute is increased, and the reflex move- 

 ments become somewhat more complicated; but the differ- 

 ences are slight as compared with those seen in the animal 

 which has the 'tweenbrain and midbrain in addition to the 

 hindbrain and cord. 



7. The behavior of a frog with spinal cord, bulb, midbrain, 

 and 'tweenbrain ; that is to say, a frog with the entire nerv- 

 ous system exclusive of the forebrain, or cerebrum. The 

 following points are especially noteworthy : (1) the sitting 

 posture maintained at rest; (2) balancing movements; and 

 (3) more complicated movements of locomotion. 



(1) Such a frog, unlike those already described, sits erect 

 exactly like a normal frog; and this fact shows that com- 

 plete maintenance of the normal posture requires the coopera- 

 tion of higher portions of the nervous system than the bulb 

 and spinal cord, but does not involve the cooperation of the 

 cerebrum. 



(2) If the frog be placed on a rectangular block of wood, 

 and the block slowly turned so that the frog tends to slip 

 off backwards, it will crawl up and over the descending 

 edge, keeping itself perfectly balanced. By continuing to 



