444 THE INTERNAL STRUCTURE 



situation on the outer side of the great transverse fissure of the 

 braiti seems to cut it off from the Thalamus. The connection, 

 however, is effected by ihe fibres of the Foi-nix, which, as is well 

 known, arise from the Thalamus, make a figure-of-8 turn in the 

 corpora albicantia, then take the circuit upwards, and then back- 

 wards, described by this body [i.e., the Fornix], and pass to the 

 Hippocamj)us in the t^uia." 



3.— The Microscopic Anatomy of the Cerebral Con- 

 volutions. 



It has been already stated that the Convolutions differ 

 much as regards their relations to one another, to the 

 Central Ganglia, and to the fibres of the Crus. 



All the Convolutions, however, present certain common 

 characters. When a section is made through either one 

 of them in a direction transverse to its long axis, a stem 

 or projection of white matter is seen continuous with the 

 * white substance ' of the hemisphere. Externa] to this 

 white substance, a superficial layer of Grey Matter exists, 

 having an average thickness of about one-fourth of an 

 inch, which is continuous over the whole external surface 

 of the Hemisphere — since it lines the * sulci ' as well as 

 the Convolutions (fig. 158). 



This layer of cortical Grey Matter, has a greater depth 

 over the frontal and parietal than over the occipital con- 

 volutions. Its specific gravity, moreover, varies in these 

 situations, being often three or four degrees higher in the 

 occipital than it is in the frontal region (10B2 : 1028) — 

 whilst that of the parietal convolutions is more or less 

 intermediate. 



In the grey matter of the Occipital Lobe, especially that 

 of the Convolutions of its inner and inferior surface, a dis- 

 tinct lamination is generally very apparent, either to the 

 naked eye or with the aid of a pocket lens. These con- 



