- a crossing or decussation, as that of the optic nerves at the base of the brain.
- a point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis.
- the cross-shaped connection produced by the crossing over of pairing chromosomes during meiosis
- the crossing over of two parts or structures, such as the fibres of the optic nerves in the brain
