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HAND-BOOK OF PHYSIOLOGY. 



same or neighboring parts, (d.) The portions of the brain intervening 

 between these motor centres are inexcitable by similar means. 



With regard to the facts above mentioned, all experimenters are 

 agreed, but there is still considerable diversity of opinion as to their ex- 

 planation. 



FIG. 341. 



FIGS. 341 and 342. Brain of dog, viewed from above and in profile. F, frontal fissure, sometimes 

 termed crucial sulcus, corresponding to the fissure of Rolando in man; S, fissure of Sylvius, around 

 which the four longitudinal convolutions are concentrically arranged; 1, flexion of head on the neck, 

 in the median line; 2, flexion of head on the neck, with rotation toward the side of the stimulus; 3, 4, 

 flexion and extension of anterior limb; 5, 6, flexion and extension of posterior limb; 7, 8, 9, contrac- 

 tion of orbicularis oculi, and the facial muscles in general. The unshaded part is that exposed by 

 opening the skull. (Dalton . ) 



It is evident that the spots marked out on the cortex are not strictly 

 speaking motor centres, for they can be removed entirely without destroy- 

 ing the power of voluntary motion. 



Burdon-Sanderson has shown that electric stimulation of different 



