PRIMITIVE GIGANTOPYRAMIDAL FIELD BURIED IN DEPTH OF CINGULATE SULCUS OF HUMAN-BRAIN

By stereomicroscopy of a complete series of pigment preparations up to 1000 .mu.m thick, a gigantopyramidal area in the grain of man was described, which lay in front of the primary motor field on the medial surface of the hemisphere and was 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 displayed the field approximately within the limits of the commissura anterior and the corpora mamillaria, where it occupied 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 did not fuse with the primary motor area and was evidently more primitively organized than the precentral motor field. Structural details betrayed an intimate relationship between this gigantopyramidal field and the archipallial proisocortex. There was a gradation, i.e., 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 recongnizable within it, such as an accentuated external granular layer, a dense and broad lamina pyramidalis and a band-like appearance of layer Va.