THE CORTEX OF THE FORE-BRAIN, ETC. 65 



ri 



ceptibly into the third layer (5), which contains the large corti- 

 cal pyramids. The next layer (4} consists of smaller and irregu-S-4. 

 larly pyramidal cells. Possibly, however, these may be similar ^^ 

 to those lying more superficially, except that they have not 

 reached their full development, for they lie wedged in between " 

 the masses of medullary fibres which pass into the cortex^ 

 These fibres, after reaching the cortex, break up into numerous 

 fine fibrils, and are gradually lost in finer and more superficial 

 net-works, or become continuous with the axis-cylinders of the {^-^- t -~ => 

 cells. Aside from these we? see vast numbers of other medullated 

 nerve-fibres in the cortex. Whence they come or whither they 

 go is still utterly unknown. 



Even though the explanation of the ultimate mechanism 

 of the organ of mind is wanting, still we have of late years 

 come nearer to it, chiefly by means of the finer technical methods 

 in use. As long as we cannot give all these fibres a name cor- 

 responding to their function, it will be better for the sake of 

 clearness (for instance, in researches in pathological anatomy) 

 to give them provisional names. Let us distinguish (1) radiati 

 medullary fibres, (2) inter-radial net-work consisting mostly of 

 fibres parallel to the surface, (3) super-radial net-work, and (4) 

 tangential fibres. Along the boundary between the inter-radial 

 and super-radial net-works the former becomes markedly thick- 

 ened. This layer, everywhere visible as a white line, is so 

 strongly marked in the vicinity of the cuneus as to be easily 

 recognized. It is called the line of Gennari or, after its later 

 describers, the line of Baillarger, and, in the vicinity of the 

 cuneus, the line of Vicq d'Azyr. In the occipital lobe this line 

 lies deep in the third layer, nearer the fourth than is shown in 

 Fig. 37, which represents the frontal lobe. 



As was previously stated, the cortex has not the same struc- 

 ture at all points of the surface. Besides the peculiarities im- 

 parted to it in the vicinity of the calcarine fissure by the line of 

 Gennari, the cortex of the gyms hippocampi presents a character- 

 istic appearance on account of the involution in the region of the 



