624 



PHYSIOLOGY OF THE BRAIN-STEM 



Briefly stated, every action of the pigeon without a cerebrum gives the 

 observer a peculiar but perfectly unmistakable impression of an automaton. 

 Its actions are very diverse and very complicated, but under given circum- 

 stances can be very definitely predicted with a high degree of certainty. The 

 decerebrated bird moves therefore in a world of objects, the position in space, 

 size, configuration of which determine the character of its movements, but 

 which are otherwise entirely without meaning to the bird. One thing like 

 another is a mere space-filling mass : it avoids or pushes aside another pigeon 

 as it would a stone. A cat or a dog means no more than an inanimate object. 



A decerebrated male coos like a 

 normal male and exhibits evi- 

 dence of sexual desire but his 

 affections are entirely objectless. 

 It appears to be a matter of in- 

 difference to him whether a fe- 

 male is present or not. In the 

 ^ same way a female shows no in- 

 y-^i^^r' terest i n ] ier young. If full- 

 fledged, they follow the mother, 

 screaming incessantly for food; 

 but they might as well address 

 their entreaties to a. stone. 



The functions left, however, 

 are very important ones. To 

 what extent they depend upon 

 the 'tweenbrain cannot, for want 

 of critical attention to this 



& 



FIG. 280. Lateral view of the dog's brain, showing 

 the different lobes of the cerebrum, after Ellen- 

 berger and Baum. 1, Olfactory lobe; 2, bound- 

 ary between the olfactory and frontal lobes; 3, 

 boundary between the frontal and parietal lobes 

 (cruciate fissure); 4, olfactory tract; 5, piriform 

 lobe; 6, frontal lobe; 7, parietal lobe; 8, temporal 

 lobe; 9, occipital lobe; 10, cerebellum; 11, 

 boundary between the parietal and temporal 

 lobes (fissure of Sylvius) ; 12, medulla oblongata. 



point, be definitely stated. But 



from Schrader's observation that animals in which the optic thalami were in- 

 jured extensively in removing the cerebrum stumbled over very slight obstacles 

 and did not correct the positions of their limbs immediately when they were 

 displaced, it seems probable that the 'tweenbrain plays an important role in all 

 these functions. 



Among mammals we have observations on the complete removal of the 

 cerebrum from rabbits and dogs (Figs. 279 and 280). 



According to Christiani, rabbits with the cerebrum removed sat immedi- 

 ately after the operation just as normal animals are careful to sit, and when 

 attempts were made to catch them by the hind leg they ran. Spontaneous move- 

 ments were also occasionally made. But when they were not disturbed in any 

 way and were protected from powerful stimuli, they easily fell asleep. They 

 woke from this sleep without being roused externally. They walked about for a 

 long time but finally came to rest and went to sleep again. There was nothing 

 abnormal in any of these movements: the animals avoided obstacles without 

 touching them ; they made stops in the midst of their wanderings ; they climbed 

 and sprang upon objects; etc. 



The rabbit therefore can also regulate its movements quite normally with- 

 out a cerebrum and can use its visual sense for this purpose. We have no 



