FUNCTIONS OF THE BRAIN-STEM AS A WHOLE 



621 



We may conclude that in fishes and frogs the central nervous system up 

 to and including the 'tweenbrain is sufficient to regulate all the animal's 

 functions (with the exception, of course, of those directed by the sense of 

 smell) just as in the normal animal. Noticeable changes are produced in 

 the behavior of the dogfish after removal of the 'tweenbrain and the midbrain, 

 in the frog only after injury to the 'tweenbrain. 



After taking out the cerebrum of a lizard (Fig. 277), Steiner observed no 

 other result than loss of spontaneous ingestion of food and of voluntary move- 

 ments. When stimulated the animal moved in a perfectly normal manner, 

 avoided obstacles, climbed up the wall of 

 the cage, exhibited no disturbance of the 

 muscular sense, etc. On the other hand it 

 would no longer try to escape when threat- 

 ened. Likewise, when the cerebrum and the 

 'tweenbrain both are removed, the lizard can 

 still make perfectly normal movements in- 

 cluding leaps of large size. It appears, how- 

 ever, to become quiescent sooner and its 

 movements in climbing seem less accurately 

 regulated than in the animal with the 'tween- 

 brain intact. 



The turtle without a cerebrum differs 

 only a little from the normal animal. It 

 makes spontaneous movements, reacts like a 

 normal animal to light rays and is able to 

 estimate visual impressions properly for its 

 own advantage. It is uncertain, however, 

 whether such an animal takes food sponta- 

 neously. One such animal, it was observed, 

 left tadpoles placed in its cage untouched 

 for as long as three days. Since, however, 

 an animal whose olfactory nerves only were 

 cut did the same thing, it is possible that 

 here as with the dogfish the determining 

 factor is the sense of smell. 



In extirpating the 'tweenbrain from the 

 turtle, it is necessary to destroy the optic 

 nerves; hence the result of the operation is 

 blindness. Nevertheless the animal is able 

 to orient itself in space excellently, and, 

 although it seldom does so, to move spon- 

 taneously. Some slight abnormalities also 

 are exhibited in its gait and in the manner 

 of its carriage. 



Finally, when the midbrain in addition 

 to the cerebrum and 'tweenbrain are re- 

 moved, a remarkable phenomenon, first observed by Fano, ensues namely, an 

 uncontrollable impulse to move about (cf. the similar behavior of the frog, page 

 604). The animal creeps incessantly in an aimless way; goes back and forth 

 from land to water and from water to land apparently without ever finding a 

 comfortable place. There are, however, unmistakable abnormalities in its move- 



Forebrain 

 (hemispheres) 



Pineal body 

 (part of 

 'tweenbrain) 



Midbrain 

 (optic lobes) 



Hindbrain 

 (cerebellum) 



Afterbrain 

 (medulla 

 oblongata) 



Ned 



FIG. 277. The brain of a lizard (Hatteria 

 punctata), after Wiedersheim. The 

 cranial nerves are indicated by 

 Roman numerals. 



