Ambiguity surrounds the existence and morphology of the human forniceal commissure. We combine advanced in-vivo tractography, multidirectional ex-vivo ﬁber dissection, and multiplanar histological analysis to characterize this structure’s anatomy.
Across all 178 subjects, in-vivo ﬁber dissection based on the Human Connectome Project 7 T MRI data identiﬁes no interhemispheric connections between the crura fornicis. Multidirectional ex-vivo ﬁber dissection under the operating microscope demonstrates the psalterium as a thin soft-tissue membrane spanning between the right and left crus fornicis, but exposes no commissural ﬁbers. Multiplanar histological analysis with myelin and Bielchowsky silver staining, however, visualizes delicate cruciform ﬁbers extending between the crura fornicis, enclosed by connective tissue, the psalterium.
The human forniceal commissure is therefore much more delicate than previously described and presented in anatomical textbooks.
This ﬁnding is consistent with the observed phylogenetic trend of a reduction of the forniceal commissure in non-human primates compared to non-primate eutherian mammals.