[TA] although classified as a cranial nerve, the optic nerve is actually an extension of the forebrain; it conveys afferent fibers from the ganglion cells of the retina, and it passes out of the orbit through the optic canal to the chiasm, where a portion of the fibers cross to the opposite side in the optic chiasm; crossed and uncrossed fibers pass through the optic tract to the geniculate bodies, superior colliculus, and pretectum. SYN: nervus opticus [CN II] [TA], second cranial nerve [CN II].