ix MID- AND INTER-BRAIN 497 



Even when the mid -brain as well as the 'tween -brain is 

 destroyed, there is, according to Bethe, no disturbance of the 

 spontaneous movements ; the dog-fish is still capable of perfectly 

 equilibrated movements, which differ in no way from those of the 

 normal animal. 



Marked disorders of movements only appear after removal of 

 the mid- and hind-brain ; the results of Steiner, Loeb, and Bethe 

 all agree on this point. The roof of the mid-brain is not 

 concerned in the movements, and it can be extirpated on one or 

 both sides without producing any motor disturbance, but accord- 

 ing to Steiner the animal no longer reacts to light stimuli. 

 Removal of the ventral part of the mid-brain, on the contrary, 

 produces constant motor disturbances, which are specially marked 

 after unilateral section. 



If the whole of the right side is divided at the posterior edge of 

 the mid-brain, the animal swims directly after the operation in 

 circular progression to the left. Sometimes these circus move- 

 ments are associated with rotation round the long axis. 



After total separation of the mid- and hind-brain, the animal 

 usually exhibits circus movements to either side, but if the lesion 

 is quite symmetrical, it advances in a straight line, and turns and 

 changes its direction only on coming in contact with the vessel 

 walls. Moreover, it changes from the horizontal plane into an 

 oblique or vertical direction only under external stimulation, and 

 during such change it may for a time take up the abnormal 

 position with its back downwards, though finally it turns over 

 briskly to assume the abdominal position: To conclude, the dog- 

 fish without its mesencephalon executes perfectly normal swimming 

 movements, but has difficulty in altering the direction of its 

 movements, while orientation in space is affected but not lost. 

 According to Bethe, Steiner is mistaken in stating that the animal 

 is incapable of spontaneous movements under these conditions, and 

 that artificial stimuli are necessary to rouse it to locomotion. 



IV. We must next consider the effects of destroying the brain 

 in Amphibia, and, first of all, in the frog (Fig. 253). 



Goltz 1 assumed (1869) that absence of voluntary locomotor 

 movements was the most important point in which the animal 

 that had lost its fore -brain differed from the intact animal. 

 Obviously, however, he excised the optic thalamus or mid-brain 

 together with the fore-brain. When the functions of these two 

 separate parts of the brain are distinguished, as was achieved by 

 Goltz' pupil M. Schrader (1887), the results are very different, for 

 if the optic thalami are interfered with as little as possible the 

 animal differs in no respect from the intact animal. The frog 

 moves spontaneously, even when placed in an unnatural position ; 



1 In his monograph, " Beitrage zur Lehre von den Funktionen der Nervenzentren 

 des Froschfs." 



VOL. Ill 2 K 



