decussation

noun

1. a process of becoming or condition of being crossed in the form of an X.
2. Anatomy. a nerve or tract of nerve fibers that crosses from one side of the central nervous system to the other.

n.

1. A crossing in the shape of an X.
2. An X-shaped crossing, especially of homonymous nerves or bands of nerve fibers, connecting corresponding parts on opposite sides of the brain or spinal cord.