OOETEX OF FOKEBKAIN AND MEDULLA OF HEMISPHERES. 337 



by its appearance in an abnormal place, but also by the thickness of its fibers, which 

 by far exceed the otherwise normal fibers. Only in extreme age, where — probably 

 in consequence of the senile cachexia — there is somewhat more neuroglia in the cere- 

 bral cortex, do such fibers occur. Where many of the glia-platelets cross, there arise 

 the astrocytes and "'cells'' of Deiter, which are very frequently met with, therefore, 

 in paralyses. 



As exact a knowledge as is possible of the cerebral cortex is justly striven for 

 in all directions. Psychiatry can boast pleasing results which have come from studies 

 in this field. I will only mention the discovery of Tuczeck, who demonstrated that 

 in the progressive paralyses of the insane the net-work of nerve-fibers in the first 

 layer was the first to degenerate, and that the fibers in the deeper layers then suc- 

 cessively disappear as far as into the fourth. A similar process has later been proved 

 for other psychoses, and more recent discoveries have shown that in the deeper parts 

 of the brain also a degeneration of fine fibers occurs in paralyses. This is here and 

 there occasioned, as the course of its spreading allows us to infer, through the sec- 

 ondary degeneration of fibers interrupted in the cortex. 



The nerve-fibers in the cerebral cortex become medullated only very late. 

 Medullation occurs in the ninth month of fetal life first of all in the superior 

 parietal lobule and in the posterior central gyrus; in the first month of extra-uterine 

 life single fibers in the anterior central gyrus are added to these; later, in the sec- 

 ond and third months, the process begins in the occipital lobe of the cortex. It is 

 probable that these events stand in relation to the time at which man begins to 

 store up impressions in the separate regions of the brain; that, for example, with 

 the acquisition of visual perception, the optical centers of the cortex first begin their 

 development. 



In later life more extended regions are constantly becoming medullated (see 

 page 231). 



The white medulla of the hemisphere lies beneath the cortex. This 

 homogeneous white substance, revealed to the naked eye by a section through 

 the centrum semiovale, is resolved by the microscope into a large number 

 of fibers crossing one another in various directions, but the separate fibers 

 are traced only with difficulty. Let us endeavor, so far as at present possible, 

 to become acquainted with these fibers. 



If sections are made through the fresh brain of a newborn child, it 

 will be seen that there lies almost everywhere beneath the cortex a peculiar 

 grayish-red, transparent mass, in which white nerve-fibers are to be found 

 at one small spot only: beneath the upper portion of the posterior central 

 gyrus and in its neighborhood. In the course of the first months of life 

 other nerve-tracts become medullated: first of all those tracts mostly which 

 pass downward from the cortex; soon, however, tracts also that connect sepa- 

 rate cortical regions with one another. 



The latter, the fihrce propriw of the cortex, are exceedingly numerous in 

 the adult brain; they everywhere extend from gyrus to gyrus, connecting 

 distant gyri and those adjacent to one another. They also connect entire 

 lobes. Apparently these "association-fibers" arise only in consequence of 

 the association of two cortical regions in a common action; in other words. 



