Incomplete decussation such as occurs in the human optic chiasm.


(sĕm″ē-dē″kŭs-sā′shŭn) [″ + decussare, to make an X]
Incomplete crossing of nerve fibers.


The rearrangement of the fibres of the optic nerves occurring in the optic chiasma in which about half of them from each optic nerve pass on to the contralateral optic tract. Thus each optic tract contains one half of the fibres of the ipsilateral optic nerve (representing the ipsilateral half visual field) and one half from the contralateral optic nerve (representing the contralateral half visual field). Syn. semidecussation. See decussation.