182 Cortex of the Fissura Hippocampi [CHAP. 



sight it might be supposed that the two sets of cells are identical ; but closer inspection 

 proves this to be incorrect, for the cells of the subicular region not only differ in form, 

 being much longer, but the body is distinctly smaller, also the substance of the cells stains 

 much more intensely, and the nucleus is smaller. 



Distribution. 



Being coterminous with the cortex of the lobus pyriformis on the one hand, and with 

 that of the gyrus dentatus on the other, the distribution of this type of arrangement is best 

 described as covering the wall and lip of the fissura hippocampi. It only remains to be 

 observed that in the posterior direction it continues well up behind the splenium, there to 

 join the post-limbic cortex ; and concerning the latter, it is important to mention that it 

 also is characterised by a remarkably deep and well-developed zonal layer, especially in the 

 immediate neighbourhood of the corpus callosum. 



STRUCTURE OF THE GYRUS DENTATUS. 



The structure of the invaginated cortex of the gyrus dentatus has been studied carefully 

 by various histologists, and a faithful account of the curious arrangement of its contained 

 elements is to be found in any text-book of histology, hence there is no necessity for me 

 to describe it at length. I need only mention that the most important elements in this 

 region are unquestionably the large pyramidal cells to which I have already briefly alluded, 

 and that the minute cells of the well-known stratum granulosum constitute a remarkable but 

 less important feature. 



One or two points of interest concerning the distribution of the curious large pyramidal 

 cells must be mentioned. In the first place, inspection of serial sections shows that they 

 extend all along the part known to anatomists as the gyrus dentatus ; then in the anterior 

 direction, as I have already indicated, such cells find a place in the substance of the 

 recurved uncus proper ; posteriorly also they have an interesting distribution, for they do 

 not end in the subsplenial part of the gyrus dentatus, but are continued round the splenium 

 corporis callosi, and gradually becoming reduced in numbers and also in size they finally 

 seem to pass on into the striae longitudinales mediales. 



STRIAE LONGITUDINALES MEDIALES OR NERVI LANCISII. 



I include a reference to these striae, not because of any supposed functional value they 

 possess, but on account of the supposition that they represent the undeveloped remains of 

 what is cortex in the brains of osmatic animals 1 . 



In the human brain transverse sections show that the cortex of the gyrus fornicatus 

 is continued in the mesial direction over the surface of the corpus callosum in the form 

 of an exceedingly thin lamina known to anatomists as the indusium griseum ; at the angle 

 of junction a slight and unimportant elevation composed of nerve fibres, the ligamentum 



1 From Zuckerkandl and other comparative anatomists we learu that these striae are the relics of two super- 

 added gyri arranged concentrically round the corpus callosum, between it and the gyrus fornicatus; the tirst of these 

 placed on the dorsum of the corpus callosum is called the gyrus supracallosue, and it is said that with the naked 

 eye it may be seen to be continuous with the gyrus dentatus ; the second envelops the genu, it is known as the 

 gyrus geniculi, and is said to be connected with the septum lucidum. 



