Introduction: Based on the study of the vascular anatomy of craniopagus twins, and particularly that of Ladan and Laleh, a theory is hypothesised regarding the embryological formation of the sagittal sinuses.
Theory and discussion: The superior sagittal sinus develops in contact with the calvarium bone within the inter-periosteal leptomeningeal space following a signal from the midline of the telencephalic vesicle derived from a single prosencephalic one. The position of the falx cerebri and most likely in the deepest part, the corpus callosum, points to the position of this midline.