226 ANATOMY OF THE OENTBAL NEEVOUS SYSTEM. 



observed. As a rule, the sense of touch at first appears to be blunted so far as the 

 judgment of what is felt comes in question, but very slight stimuli may be recog- 

 nized as tactile irritants if they are of a, very simple nature (as touching with a 

 downy feather, needle-point, etc.). Areas of the cerebral cortex from which disturb- 

 ances of sensibility arise more frequently than from lesion of others are not definitely 

 kno^^■n. At all events, such disturbances may appear after lesions situated in the 

 territoiy of the central gyri and their neighborhood. It is veiy probable that lesions 

 of the cornu Animonis, perhaps of the remaining parts of the marginal gyrus also, 

 may produce disturbances in the sense of smell. 



The paralyses that arise from affections of the cerebral cortex alone are never 

 so complete as those produced by the destruction of the peripheral nerves or their 

 proximal ends in the spinal cord. In animals it is generally impossible to obtain 

 permanent paralyses by the removal of the cortex in the motor zone, or the removal 

 of the entire portion of the brain that contains this zone. Nevertheless, upon irrita- 

 tion of circumscribed areas of the cerebral cortex in these same animals the same 

 muscles may nearly always be made to contract from the same cortical area. 



And now, having become acquainted with the location of the cortical centers 

 in man, let us cast a glance at the illustrations shown in Fig. 149. They show, ac- 

 cording to the experiments of Mann, what parts of the surface of the mammalian 

 brain are at present known to have a, definite function. 



This leads us back to what was said in the twelfth chapter respecting the sig- 

 nificance of the mantle as a collection of individual centers and areas of associa- 

 tion. It is immediately recognized that much that is found in the brain of Primates 

 is not present at all in the lower mammals, or is so small as not to be demonstrable. 



For a better understanding of the physiological status of the mantle of 

 the brain, consider again what was presented on page 173, and, moreover, 

 recollect the experiments of Ewald, mentioned on page 44. These show 

 that many things are necessary for the orderly execution of the acquired 

 movements, and that, where lesions exist, one factor or another may occa- 

 sionally compensate for what was lost. 



It may truly be said that the mantle of the brain increases in mass as, 

 ascending in the vertebrate series, new centers are established in it: cortical 

 areas that are concerned in the execution of movements for the inhibition, 

 recognition, and interpretation of sensory impressions, and, probably in a 

 large measure, for association also. 



