68O FUNCTIONS OF THE CEREBRUM. [CH. XLVIII. 



occurs in the Rolandic area is a sense of movement, and this acts 

 as a stimulus via the pyramidal tracts to the true motor centres 

 which are in the opposite anterior horn of the spinal cord. If the 

 posterior roots of the spinal nerves are divided there is a loss of 

 sensation, and so the sense of movement cannot reach the brain 

 from the muscles, and consequently the muscles are not called 

 into action ; when all the posterior roots coming from a limb in 

 a monkey are cut, the muscles, so far as voluntary movements 

 are concerned, are in fact as effectually paralysed as if the 

 anterior roots of the spinal nerves had been cut. The muscles, 

 however, do not degenerate as they would if the anterior roots 

 had been cut. They merely undergo a small amount of wasting 

 due to want of use ("disuse atrophy "). 



The question will then be asked, what is the function of the gyrus 

 fornicatus 1 On removal of this convolution there is some loss of 

 sensation ; this has been explained by the fact that on removing 

 this area of grey matter it is almost impossible to avoid injury to 

 the white matter beneath it, and thus there will be loss of function 

 due to division of the fibres on the way to the marginal convolu- 

 tion, which is like the Rolandic area, sensori-motor in function. 



Prof. Schafer is one prominent worker who has not accepted 

 Munk's views on this subject. He still regards the Rolandic 

 area as essentially motor in function. Naturally, he does not 

 deny that it has connections with sensory fibres, but he considers 

 it incorrect to speak of the area as a sensory one. He has 

 produced injuries of the area without obtaining any loss of 

 sensation, and in testing the sensations of his' monkeys employs 

 the method of stroking the skin, which he regards as more trust- 

 worthy than Schiff's clip test. The sensory disturbances observed 

 by other investigators he regards as due to general disturbance of 

 the whole brain produced by the severity of the operation. The 

 exact localisation of the tactile areas must be left to the future, 

 as in his most recent experiments Schafer has failed to confirm 

 his earlier ones on the gyrus fornicatus. 



On referring once more to the maps of the brain, it will be 

 seen that there is a large blank in the anterior part of the frontal 

 region. This is left blank because its function is absolutely un- 

 known. Extirpation or stimulation of this part of the brain in 

 animals produces no appreciable result. It has also been removed 

 accidentally in man, as in the celebrated American crowbar acci- 

 dent ; owing to the premature explosion of a charge of dynamite 

 in one of the American mines, a crowbar was sent through the 

 frontal region of the foreman's head, removing the anterior part 

 of his brain. He, however, recovered, and no noteworthy 



