FUNCTIONS OF THE BEAIN. 



815 



body it may be made to leap ; when placed on its back it regains its 

 normal attitude. When placed on an inclined plane it crawls up until it 

 gains a new position, and if such an experiment be made by placing a 

 frog on a small piece of board, by gradually inclining the board more 

 and more the frog may be made to climb up the board, pass over to the 

 other side, and the piece of wood may be turned over a number of times, 

 the frog always moving with it as long as its equilibrium is dis- 

 turbed. Such a frog will likewise be apparently sensible to light, and if 

 made to jump will avoid objects casting a strong shadow. Such move- 

 ments as above described are evidently carried out by co-ordinating 

 mechanisms and governed by definite afferent impulses (Figs. 355 and 

 356). 



It is evident, from the existence of these motions in the frog 

 deprived of its cerebral hemispheres, that the mechanism governing 

 them must lie in parts of the central nervous system below the line of 

 section. No such operations can be effected in a frog in which the 

 medulla has been removed. It follows, therefore, that in the medulla, 

 or perhaps in the corpora quadrigemina and optic lobes, are found the 

 co-ordinating centres of the most complex muscular movement. 



FIG. 3.55. FROG WITHOUT ITS CEREBRUM 

 AVOIDING AN OBJECT PLACED IN 

 ITS PATH. (Landois.) 



FIG. 356. FROG WITHOUT ITS CEREBRUM 

 MOVING ON AN INCLINED BOARD, 

 AFTER GOLTZ. (Landois.) 



In the mammal or bird a similar state of affairs is present, although, 

 as might be expected, complicated to a greater degree by the more 

 severe shock of the operation. 



In a bird or a mammal in which the medulla remains after removal 

 of the cerebral lobes the attitude may become perfectly normal. If 

 placed on its side it will regain its feet. If a bird be thrown into the 

 air it will fl}- for a considerable distance, perhaps avoiding obstacles, but 

 its movements more resemble those of a stupid, sleep3 T animal than one 

 in full possession of its faculties. A mammal, also, so operated on can 

 stand, run, and leap, and if placed on its back can regain its normal 

 position, but if left alone it remains absolutely motionless. If food is 

 placed in the mouth of the animal in whom ablation of the cerebrum 

 has been successfully performed the animal will eat, and the complicated 

 motions of mastication and deglutition will be accomplished with perfect 

 regularity. 



