686 FUNCTIONS OF THE CEREBRUM [CII. XLVIII. 



and thoroughly explore it with a weak faradic current, one electrode 

 being placed on the brain, and the other attached to an indifferent 

 part of the animal's body. This allows of finer localisation than is 

 possible with the ordinary double-point electrodes. 



The so-called "motor" area includes continuously the whole 

 length of the ascending frontal, or as it is sometimes called, the pre- 

 central convolution. It never extends behind the central sulcus, or, 

 as it is sometimes called, the fissure of Eolando. On the mesial 

 surface it extends but a short distance, and never as far as the 

 calloso-marginal fissure. The motor area extends also into the depth 

 of the Eolandic and other fissures; the part of the excitable area 

 thus hidden equals or may even exceed that on the free surface of 

 the hemisphere. The arrangement of the various regions of the 

 musculature follow the segmental sequence of the cranio-spinal series 

 to a remarkable extent ; in fact, the excitable area may be compared 

 to the spinal cord upside down. The accompanying figure indicates 

 this better than any verbal description. 



The sulci in the region of the cortex dealt with cannot be con- 

 sidered to act as physiological boundaries, and the variations in the 

 sulci in these higher brains are so great that they prove to be pre- 

 carious or even fallacious landmarks to the details of the true 

 topography of the cortex. 



It cannot fail to strike even a superficial observer how large 

 the cortical area is that deals with movements of the head and arm 

 regions when compared with that of the lower limb, and still more 

 with that of the trunk. The trunk itself has a larger mass of 

 muscular tissue, but it is in the head region (which includes the 

 complex movements of the tongue and such structures as the vocal 

 cords) and in the arm and hand that the movements are most varied 

 and most delicate. No doubt this is the explanation of the greater 

 size of their cortical representation. 



The experiments of extirpation confirm those of stimulation ; for 

 example, extirpation of the hand area is followed by severe paralysis 

 of the hand, but in a few weeks use and power return in a remarkable 

 degree. On the other hand, ablations of even larger portions of the 

 parts behind the Eolandic fissure do not give rise to even transient 

 paralysis, and do not lead to degeneration in the pyramidal system 

 of fibres. 



Sherrington and Griinbaum also found that the part of the frontal 

 region which yields conjugate movements of the eyeballs is separated 

 from the Eolandic area by a field of " inexcitable " cortex. As to the 

 occipital lobe, only from its extreme posterior apex did faradisation 

 yield any movement of the eyes, and then not easily. This becomes 

 intelligible on histological examination ; the large motor cells in the 

 deeper layer of the grey matter are so scattered that they are called 



