A primitive gigantopyramidal field buried in the depth of the cingulate sulcus of the human brain.

By stereomicroscopical examination of a complete series of pigment preparations up to 1000 mum thick, a gigantopyramidal area in the brain of man is described, which lies in front of the primary motor field on the medial surface of the hemisphere and is almost totally buried in the depth of the cingulate sulcus extending in both length and width over about 15 mm. Serial sections cut in the transverse plane display the field approximately within the limits of the commissura anterior on the one hand and the corpora mamillaria on the other, where it occupies large parts of the dorsal wall of the gyrus cinguli (lower bank of sulcus cinguli) and a small area of the adjacent superior frontal gyrus. The sharply outlined field does not fuse with the primary motor area and is evidently more primitively organized than the precentral motor field. Structural details betray an intimate relationship between this gigantopyramidal field and the archipallial proisocortex. We could clearly trace a gradation, that is, a stepwise change of architectonic features in constant orientation from the limbic proisocortex over a small paralimbic transition zone to the gigantopyramidal field, accounting for the numerous limbic traits recognizable within it, such as, for instance, an accentuated external granular layer, a dense and broad lamina pyramidalis, and a band-like appearance of Va.