652 PHYSIOLOGY OF THE CEREBRUM 



From the summaries of clinical cases of this character it appears with 

 perfect definiteness, however, that so far as these particular disorders are 

 concerned, lesions of the occipital, temporal, and the greater part of the frontal 

 lobes are of no consequence; that therefore the cortical field, lesion of which 

 is accompanied by loss of general sensation and touch embraces the central 

 and parietal convolutions, the paracentral lobule and possibly the posterior 

 part of the frontal convolutions. 



More detailed study of cases appertaining to this subject appears to show 

 further that the anterior central convolution, the importance of which as a 

 place of origin for the long-fibered efferent tracts was discussed at page 633, 

 can be thrown out of function without entailing any loss of general sensa- 

 tion, that therefore the sensory cortical area consists for the most part of the 

 posterior central and the parietal convolutions. The disturbances to the dif- 

 ferent modalities of sensation resulting from lesions within these parts of the 

 cortex appear to be rather different in degree. The pain sensations suffer 

 least; the pressure and temperature sensations are said to be somewhat re- 

 duced, but are not by any means always abolished. The power of localization 

 is very profoundly affected and the patients make very great mistakes when 

 tested for this sense. The motor sensations are likewise much disturbed; 

 patients can neither recognize the exact position of their limbs nor tell when 

 they are moved passively. Whether there is any dependence of the modality 

 affected upon the exact place of the lesion within the general region, we can- 

 not say definitely at present. 



Further proof of the functional relations here indicated is found in the 

 anatomical discoveries concerning the convergence of the conducting path- 

 ways of the tactile and other general sensory nerves into the cerebral cortex. 

 As Flechsig has pointed out, these for the most part enter the posterior central 

 convolution and only a small fractional part of them reaches the anterior 

 central. Besides, the paracentral lobule, the first frontal convolution and the 

 gyrus fornicatus also receive such fibers. But, on the other hand, the origin 

 of the pyramidal pathways is found chiefly in the paracentral lobule, in the 

 whole anterior central convolution and in the posterior part of the first frontal 

 convolution. It is significant also in view of this arrangement that the an- 

 terior central convolution, as well as the posterior part of the first and second 

 frontal convolutions, has a different structure from that of the other cortical 

 regions and that of the posterior central convolutions. The chief difference 

 consists in the enormous thickness in the former of the layers of the middle- 

 sized and the superficial giant pyramidal cells (Cajal, see Fig. 284). From 

 these relations we can understand how it is that motor paralysis of cortical 

 origin is not necessarily accompanied by loss of sensibility. 



It is also possible to convince oneself by stimulation that the region under 

 consideration is in fact a terminus of sensory nerves. If the central convolu- 

 tions of an unaesthetized man be stimulated electrically, while he feels no 

 pain there is at first an itchy, prickling sensation in that part of the body 

 whose muscles contract to the stimulus an observation which agrees with the 

 statements of patients suffering from cortical epilepsy regarding the premoni- 

 tory symptoms of epileptic attacks. 



In short, from the clinical evidence obtained on men and from experiments 



