VASCULARITY OF THE CEREBRAL CORTEX 203 
within the range of variation of the other individuals, however, 
it was decided not to discard them. 
In all the five areas studied, the lamina granularis interna 
(IV) is decidedly the richest, the lamina pyramidalis (III) 
coming next, with the lamina ganglionaris (V) very little behind 
it. The fourth in order of richness is the lamina zonalis (I), 
while the lamina multiformis (VI) is the poorest in every region 
except the insular. It may be remarked that the lamina granu- 
laris interna, which is absent from the praecentral region of many 
mammals, is distinct, though thin, in that portion of the cortex 
of the rat, and it is interesting to note that it is not relatively 
poorer in its capillary supply there than in the other areas. 
These observations may be compared with the description of 
Duret (’74) fifty years ago. He found that the outer 0.1 mm. 
of the human cerebral cortex contained large quadrangular meshes 
parallel to the surface, the next 2 mm. is filled with rather fine 
polygonal capillary meshes, while the inner 1 mm. has a transi- 
tional network with larger meshes, which, however, are much 
less elongate than those of the white matter into which they pass. 
There is little certainty at the present time regarding the 
functions of the different layers of the cerebral cortex. Bolton 
(00) noticed twenty years ago that, while the deeper layers did 
not vary appreciably in thickness as a result of age or chronic 
insanity, ‘‘there is an almost exact correspondence between the 
thickness of the conjoined first and second layers? of the cortex 
and the degree of amentia or dementia existing in the patient.” 
Nine years later, Kappers (09) concluded upon the basis of 
comparative evidence that ‘“‘the granular layer in the cortex 
is primary in character, and has originally receptive functions,”’ 
that the subgranular layers (V, VI) have chiefly the functions 
of projection and intraregional association, while the supra- 
granular layers (II, III), which are the last to appear phyletically, 
are concerned chiefly with association of a higher order (inter- 
regional), including intellectual processes. 
* The ‘second layer’ of Bolton appears to be equivalent to Brodmann’s laminae 
II and III, i.e., the supragranular layers, 
