dec·us·sa·tion 
(dĕk′ə-sāshən, dē′kə-)
(dĕk′ə-sāshən, dē′kə-)n.
1. A crossing in the shape of an X.
2. Anatomy An X-shaped crossing, especially of nerves or bands of nerve fibers, connecting corresponding parts on opposite sides of the brain or spinal cord.