XVI THE NERVOUS SYSTEM 313 



weakened condition of the limbs persisted in a marked 

 degree two and a half months after the operation (especially 

 when the frog was greatly excited)." It seems not improb- 

 able that the discrepant results of the different investigators 

 of this subject may be mainly due to differences in the 

 amount of nervous material removed by the operation. 



The conclusion of Goltz that the optic lobes and the 

 cerebellum contain the centers for locomotion cannot be 

 sustained, since Schrader and others have shown that coor- 

 dinated locomotion is still possible after the cerebellum and 

 all parts of the brain lying in front of it are destroyed. 

 According to Steiner, if the cerebral hemispheres are 

 removed along with the cerebellum, the frog shows certain 

 symptoms that do not appear after loss of the cerebral hemi- 

 spheres alone. Frogs deprived of both these parts of the 

 brain were found, when attempting to jump from one object 

 to another, either to fall short of the goal, or to jump too 

 far, whereas animals from which the cerebral hemispheres 

 alone were removed were able to adjust more accurately the 

 length of their spring. 



The Medulla. — A frog with the brain removed as far 

 back as the medulla is still capable of performing regular 

 leaps and swimming movements of the hind Hmbs. When 

 thrown on its back it rights itself, and it still performs com- 

 pensatory motions when tilted or rotated. Breathing is 

 normal, and the animal swallows pieces of food that are 

 placed in its mouth. 



If the anterior portion {pars commissiiralis) of the medulla 

 is removed, the frog becomes possessed of an uncontrol- 

 lable tendency to move about, whereas if the medulla is 

 intact, the movements of the animal are sluggish. It creeps 

 about restlessly, coming to rest only when it has arrived 

 in some protected nook or corner. Locomotion is effected 



