FUNCTIONS OF THE BRAIN. 19 



the hemispheres, that a current goes straight to the wiping- 

 arrangement in the sjjinal cord, exciting this arrangement 

 as a whole. Similarly, if an intact frog wishes to jump 

 over a stone which he sees, all he need do is to excite from 

 the hemispheres the jumping-centre in the thalami or 

 Avherever it may be, and the latter will provide for the de- 

 tails of the execution. It is like a general ordering a 

 colonel to make a certain movement, but not telling him 

 how it shall be done.* 



The same muscle, then, is repeatedly represented at different 

 heights; and at each it enters into a different combination 

 with other muscles to co-operate in some special form of 

 concerted movement. At each height the movement is dis^ 

 charged hy some particular form of sensorial stimulus. Thus 

 in the cord, the skin alone occasions movements ; in the 

 upper part of the optic lobes, the eyes are added ; in the 

 thalami, the semi-circular canals would seem to play a part ; 

 whilst the stimuli which discharge the hemispheres would 

 seem not so much to be elementarj' sorts of sensation, as 

 groups ot sensations forming determinate objects or things. 

 Prey is not pursued nor are enemies shunned by ordinary 

 hemisphereless frogs. Those reactions upon complex cir- 

 cumstances which we call instinctive rather than reflex, are 

 already :n this animal dej^endent on the brain's highest 

 lobes, and still more is this the case with animals higher 

 in the zoological scale. 



The results are just the same if, instead of a frog, we 

 take a pigeon, and cut out his hemispheres as they are ordi- 

 narily cut out for a lecture-room demonstration. There is 

 not a movement natural to him which this brainless bird 

 cannot perform if expressly excited thereto ; only the inner 

 promptings seem deficient, and when left to himself he 

 spends most of his time crouched on the ground with his 

 head sunk between his shoulders as if asleep. 



* I confine myself to the frog for simplicity's sake. In higher animals, 

 especially the ape and man, it would seem as if not only determinate com- 

 binations of muscles, but limited groups or even single muscles could be 

 innervated from the hemispheres. 



