CH. L.] THE VISUAL AREA 735 



which are tactile discriminatory, and related to position and move- 

 ment of the muscles. We still await exact information regarding 

 the cortical representation of sensations of pain and temperature. 



This conclusion regarding the sensory function of the ascending 

 parietal convolution has received support from a number of carefully 

 observed clinical cases, for Sherrington and Grimbaum's delimitation 

 to a relatively narrow strip of what had previously been considered 

 a widespread motor territory, left for some time uncertain the 

 function of the remainder of the original motor area Munk's 

 sensori-motor field lying posterior to the central fissure. The most 

 remarkable confirmatory evidence regarding the sensory functions of 

 what we may call the post-central convolution has been recently 

 afforded by two patients, who voluntarily allowed Dr Gushing of 

 Baltimore the opportunity of experimentally testing the point after 

 operations in which this part of the brain was exposed, and during a 

 time they were in a conscious state. 



In both of them characteristic motor responses were obtained 

 from the precentral gyrus (ascending frontal convolution) without 

 any conscious sensation, except that which accompanies forced change 

 of position in the parts moved. On the other hand, stimulation of 

 the post-central gyrus (ascending parietal convolution) produced no 

 movements, but gave definite sensory impressions which were likened 

 by one patient to a sensation of numbness, and by the other to 

 definite tactual impressions. 



There is, of course, a close connection between the two convolu- 

 tions in question, by short association fibres passing from one to the 

 other; and the necessity for sensation in normally provoking the 

 corresponding motor outflow is also illustrated by the following experi- 

 ment : 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 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. 



The Visual Area. The lower the animal in the series, the 

 more readily can its actions be controlled by sensory impulses which 

 have not passed through the cortex cerebri. A decerebrated bony 

 fish can distinguish colours, a frog can catch flies, even a pigeon will 

 select its perch, though it takes no notice of food or of people who try 

 to frighten it. A dog similarly operated on is practically blind, 

 though it will blink at a bright flash of light. In the lower animals 

 the impulses pass in to the primary visual centre in the optic lobes 



