Surface Contours

Abstract

The morphology of the mammalian spinal cord and brain-stem nuclei does not vary substantially among species except in size. In contrast, the surface of the cerebrum and cerebellum differ conspicuously from species to species and to a lesser degree among individuals ofthe same species. This variation in neocortical surface configuration is conferred by the arrangement of convolutions (gyri) separated by fissures (sulci). When it was recognized that the intelligent animal species possess complex brains with more convolutions and deeper sulci than do species of less intelligence, the question arose of how this came about. Was the convoluted folding a result of mechanical factors generated from fitting an enlarging cortical surface into a cranial box of relatively fixed size (“the most economical use of space”), or were there diverse functional associations that governed the directions in which the brain increased in size?

This sulcus [of Rolando] ... forms the convolutions. surest point of departure for finding the convolutions.

(Ecker, 1873, p. 8)