xvi THE NERVOUS SYSTEM 311 



hemispheres produces no such effect (Krawzoff, Kato). No 

 definite localization of motor functions such as has been 

 established in the brains of the higher mammals has yet 

 been worked out. 



Thalamencephalon. — Removal of the thalamencephalon 

 along with the cerebral hemispheres results, as before re- 

 marked, in an almost complete loss of spontaneous move- 

 ments. The animal rests quietly, and seldom makes a move 

 unless in response to some external stimulus, and shows a gen- 

 eral insensibility to touch (Loeser). Since the optic nerves 

 enter the thalamencephalon, removal of this part eauses 

 complete blindness ; the frog no longer avoids obstacles 

 placed in its path, or shows any reaction involving the power 

 of vision. When placed on a piece of wood that is slowly 

 tilted upward it will not climb to the upper side and balance 

 there, like a frog that has lost its cerebral hemispheres, but 

 it responds only by movements of the head, lowering that 

 part when the anterior part of the body is raised and rais- 

 ing it when the reverse movement is performed (Steiner, 

 Schrader). If the animal is rotated on a horizontal disk 

 it responds by turning ; soon after the operation it shows no 

 compensatory motions ; later, it responds by turning the 

 head opposite to the direction of rotation, and, after com- 

 plete recovery, performs circus movements of the body in 

 the same direction as those of the head. The same move- 

 ments are also performed after loss of the optic lobes. The 

 loss of the power to balance the body on the edge of a tilted 

 board is apparently permanent. 



The Optic Lobes. — According to Steiner the center for 

 coordinated motion is in the optic lobes. Frogs from which 

 this part of the brain was removed were found by Steiner to 

 swim with alternate movements of the legs instead of com- 

 bined strokes. Schrader showed, however, that this was the 



