EXPERIMENTS ON VERTEBRATES 



movements. It was for a long time a dogma that 

 progressive locomotive movements could only be per- 

 formed by frogs that were still in possession of their 

 cerebral hemispheres. 

 This statement was 

 made by Flourens. He 

 observed that frogs 

 devoid of the cerebral 

 hemispheres no longer 

 move spontaneously 

 (3). Later on Schra- 

 der showed that this 

 observation was not 

 correct ; that this lack 

 of spontaneity only 

 occurs when the thai- 

 ami optici are injured 

 (4). Are we to con- 

 clude from this that 

 the power of spontan- 

 eous locomotion is lo- 

 cated in the thalami 

 optici ? This would be wrong, for if the whole brain of 

 a frog including the pars commissuralis of the medulla 

 oblongata be removed, it seems " possessed of an irre- 

 sistible desire to move ; it creeps about untiringly in 

 an entirely coordinated manner and does not rest until 

 it comes to a corner of the enclosure " (Schrader). 

 It behaves like the Nereis in Maxwell's experiments 

 which was deprived of its brain. Flourens made his 



FIG. 35. THE FROG'S BRAIN. 



Gff, cerebral hemispheres; Tk.O, thalamus opticus; 

 Lob. oft, lobi optici ; A'//, cerebellum ; l^-JCf, 

 origin of the sth to nth brain-nerves. (After 

 Wiedersheim.) 



