FUNCTIONS OF THE BRAIN-STEM AS A WHOLE 623 



whether even the sense of touch were intact. But if they came through the first 

 few days, they presented quite a different picture. 



They now began to wander about and to keep up a tireless march about the 

 cage. The cadence was a moderately quick step, but frequently as the movement 

 went on it increased in frequency until it became a run, which then tapered off 

 to the usual cadence again, or was sometimes suddenly interrupted and the ani- 

 mal settled down to sleep. It appears that these restless movements were not 

 the result of any abnormal state of excitation, for the same animals which wan- 

 dered about tirelessly all day spent the night quietly in one spot. 



These movements from the first are controlled by sight, for the animal always 

 avoids obstacles about the same as a normal pigeon. They are also regulated by 

 the sense of touch and any temporary disturbance of the equilibrium is regu- 

 larly compensated by the proper motions. 



Only one reaction to auditory impressions was observed, namely that the 

 pigeon drew back at the crack of a match. Various and sundry tones and noises 

 were tried but without any apparent effect. 



But the movements of a decerebrated pigeon are readily interrupted by other 

 means: one has only to touch the animal lightly or to lift it and set it down 

 again, and it immediately draws in the head, ruffles up its feathers and falls 

 asleep. 



By specially devised experiments it is possible to show that the pigeon is 

 able to coordinate its movements to a definite end. When, for example, one 



Olfactory bulb 



Median longitudinal fissure - 



Forebrain (hemispheres) 



Midbrain (corpora quadrigemina) 



! A -i^ 



Pineal body ^' ^ 



m Hindbrain (cerebellum) 



Lateral lobe 



and 

 Vermis of cerebellum 



Afterbrain (medulla oblongata) 



FIG. 279. Brain of rabbit, after Wiedersheim. 



was placed four or five feet from the floor on a small flat surface and a perch 

 was placed one or two yards distant from it, the pigeon flew to the perch and 

 grasped it firmly with its feet. Moreover, when the pigeon was given a choice 

 between flying to the perch and flying to a table some yards farther away, it 

 very decidedly preferred the latter. 



But it never flew up spontaneously from the floor. And it could not be ascer- 

 tained positively that the decerebrated pigeon ate of its own accord. 

 37 



