IX 



MID- AND INTER-BRAIN 



499 



The effects of excising the whole of the mid-brain again differ 

 slightly, according to Schrader, from the results obtained by Goltz 

 and Steiner. When the medulla oblongata is uninjured by this 

 operation, the mutilated frog preserves its quack -reflex, and the 

 characteristic swim-reflexes, the centre for which lies not in the 

 optic lobes (Goltz and Steiuer), but in the bulb. But if the 

 animal is left undisturbed without external stimulation, the sup- 

 pression of the spontaneous movements, according to Schrader, 

 is even more definite and complete than when only the fore- and 

 mid-brain are removed. Evidently this depends not on the 

 removal of the rnid-brain as held by Goltz and Steiner, but on the 

 functional depression of the locomotor centre in the bulb, due to 



Fit:. 254. Goltz' experiment on frog deprived of its cerebral hemispheres, and made to climb up 

 and down an inclined plane. On the left the frog is seen ascending an inclined board ; in the 

 centre it has climbed to the top of the upright board ; on the right it is coming down the 

 opposite slope. 



operative traumatism. As early as 1883 Fano demonstrated that if 

 the experiment were repeated on the toad (Bufo viridis), which is 

 very near the frog in the zoological scale, but is far more resistent 

 and less excitable, a similar result is obtained as with the marsh 

 tortoise (see p. 413). After destroying the whole mid -brain 

 (including of course the 'tween- and fore-brain), automatic loco- 

 motion can be seen in this animal as readily as in the tortoise. 

 But while in the latter the locomotor movements may be con- 

 tinuous, in the toad they are nearly always periodic, viz. in the 

 form of groups of locomotor movements separated by pauses. 

 Toads, like tortoises, when deprived of the mid-brain, recover their 

 normal position by appropriate movements if turned over on 

 the back. 



Fano's studies on the marsh tortoise are of great importance, 

 as regards the results of removing the fore- and mid-brain. They 

 may be summarised as follows : Removal of the cerebral hemi- 

 spheres (Fig. 255) does not apparently deprive the animal of 

 any of the faculties attributed to the fore - brain. It moves 



