CHAP. n. J THE BRAIN. 723 



We do not wish now to discuss the details of this machinery ; 

 all we desire to insist upon at present is that, in the frog the 

 nervous machinery required for the execution, as distinguished 

 from the origination, of bodily movements even of the most 

 complicated kind, is present after complete removal of the cere- 

 bral hemispheres, though these movements are such as to require 

 the cooperation of highly differentiated afferent impulses. 



475. In warm-blooded animals the removal of the cere- 

 bral hemispheres is attended with much greater difficulties than 

 in the case of the frog. Nevertheless, in the bird the operation 

 may be carried out with approximate success. Pigeons for 

 instance have been kept alive for five or six weeks after com- 

 plete removal of the cerebral hemispheres, with the exception 

 of portions of the crura and corpora striata immediately sur- 

 rounding the optic thalami; these parts were left in order to 

 ensure the intact condition of the latter bodies. 



When the immediate effects of the operation have passed 

 off, and for some time afterwards, the appearance and behaviour 

 of the bird are strikingly similar to those of a bird exceedingly 

 sleepy and stupid. It is able to maintain what appears to be 

 a completely normal posture, and can balance itself on one leg, 

 after the fashion of a bird which has in a natural way gone to 

 sleep. Left alone in perfect quiet, it will remain impassi vi- 

 and motionless for a long time. When stirred it moves, shifts 

 its position; and then, on being left alone, returns to a natural. 

 easy posture. Placed on its side or its back it will regain its 

 feet; thrown into the air, it flies with considerable precision 

 for some distance before i^ returns to rest. It frequently tucks 

 its head under its wings, and at times may be seen to clean its 

 feathers; when its beak is plunged into corn, it eats. It may 

 be induced to move not only by ordinary stimuli applied to the 

 skin, but also by sudden loud sounds, or by flashes of light: in 

 its flight it will, though imperfectly, avoid obstacles, and its 

 various movements appear to be to a certain extent guided not 

 only by touch but also by visual impressions. 



In a certain number of cases this sleepy, drowsy condition 

 passes off and is succeeded by a phase in whieh the bird, appar- 

 ently spontaneously, without the intervention of any obvious 

 stimulus, moves rapidly about. It does not fly, that is to sav. 

 it does not raise itself from the ground in flight, but v\alks 

 about incessantly for a long while at a time, periods of activity 

 alternating with periods of repose. It seems, from time to 

 time, to wake up and move about, and then to go to sleep 

 again; and it has been observed that during the night it 

 appears to he always asleep. It is obvious, therefore, that the 

 sleepy, quiescent condition observed at tirst is not due simply 

 to the absence of the cerebral hemispheres, but is a temporary 

 effect of the operation, and that spontaneous movements, that 



