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Catani . present the corticospinal tract as a counterexample to our model of geometric structure, showing diffusion MRI that depicts corticospinal and callosal paths as crossing in a continuum of angles from 60° down to 0° angles, identical orientations, at the vertex.

Specifically, if the callosal paths express the transverse direction of a coordinate system and the projection paths as they appear in Catani . express the rostrocaudal, then they would need to remain distinct.

This implies that most white matter voxels have multiple populations of fibers where, in the same plane, thalamic, callosal, and other projection tracts merge at progressively tangential angles to reach the same cortical areas.

Conversely, studies conducted by Sperry and colleagues in the 1950s revealed greatly altered brain function in animals that had undergone callosal sections.

It will thus be seen that the hippocampal gyrus is continuous posteriorly with the callosal gyrus above by means of the isthmus, and with the gyrus lingualis below.