792 PHYSIOLOGICAL TOPOGRAPHY OF SURFACE OF CEREBRUM. 



the first. According to Flechsig the cortex is developmentally divisible into forty 

 different fields. These can be arranged in three groups: (a) The primordial 

 areas, which are formed even before mature birth; (6) intermediary areas, which 

 begin to be surrounded with medullary tissue up to one month after birth; (c] 

 the terminal areas, which are formed later than one month (from four to four and 

 a half months) after birth'. The primordial areas coincide with the sense-centers 

 in their rudimentary form; the terminal areas comprise association-areas; and 

 the intermediary areas, amplifications in part of the sense-centers and in part of 

 the association-centers. The human brain is distinguished from that of the 

 anthropoids principally through the terminal areas. They vary in size in different 

 individuals and they contribute in large measure to the shape of the human 

 skull, under the eminences of which they are situated. Thus, for example, the 

 anthropoids are unprovided with the area destruction of which causes pure alexia. 

 For this reason alone apes cannot acquire the faculty of speech. 



The motor areas comprise the anterior (Fig. 246, A) and posterior 

 (B) central convolutions, and the paracentral lobule, and extend pos- 

 teriorly into the precuneus (Fig. 262). They contain large ganglion - 

 cells, which, however, are not present before the age of one and one-half 

 months. Degeneration of the entire area causes paralysis of the opposite 

 side of the body. This at first is total, but gradually passes into a con- 

 dition in which especially all of the delicate movements under the control 

 of the will and acquired by education and exercise are abolished, while 

 associated and bilateral movements (which, for example, are present in 

 animals that after birth are at once capable of executing various complex 

 movements) are preserved more or less intact. Therefore, the hand is 

 paralyzed in man in greater degree than the arm, and this in turn in 

 greater degree than the leg, the lower branches of the facial nerve in 

 greater degree than the upper, and the nerves of the trunk finally almost 

 not at all. 



In hemiplegic individuals the strength of the unparalyzed side of the body 

 is also impaired. This is not fully explained by the fact that some 

 fibers of the pyramidal tracts remain upon the same side of the body. Among 

 the movements in human beings there are some that have to be learned with great 

 effort, and therefore gradually become subordinated to the varying impulses of 

 the will, such, for example, as the delicate movements of the hands. These 

 movements are restored but slowly and incompletely or not at all after lesions 

 of the psychomotor centers. Those movements, however, that are at once at 

 the command of the body, such as the associated movements of the eyes, the 

 face, in part also of the lower extremities, either recover rapidly after the lesions 

 described, or they appear to suffer but little at all. Thus, the facial muscles 

 appear never to be so completely paralyzed after a cortical lesion as after a lesion 

 of the trunk of the facial nerve; for example the eye can yet be closed fairly 

 well. Sucking movements have been observed even in hemicephalic new-born 

 children. 



From the motor cortical centers the path for the fibers of the facial 

 and hypoglossal nerves passes through the genu, that for the muscles of 

 the extremities through the middle third of the posterior limb of the 

 internal capsule (Fig. 263). Irritation of these paths causes movement 

 in the muscles on the opposite side. After destruction of the cortical 

 areas degeneration takes place in these corticomotor paths, which pass 

 downward and whose continuation is designated the pyramidal tracts. 

 This degeneration has been found within the white matter below the 

 cortex, in the genu, and in the anterior two-thirds of the posterior divi- 

 sion of the internal capsule, in the cerebral peduncle (middle portion of 

 the lower free circumference of the crusta, where the tracts for the ex- 

 tremities and the nerves of the trunk-muscles lie externally and those for 

 the motor nerves of the head internally), in the pons, in the pyramids 



