Along with the second pair of cranial nerves the optic chiasma and the optic tracts are described. The optic nerves are connected to the brain through the agency of the optic tracts.
Arise from the pulvinar of the optic thalamus, from the lateral and medial corpora geniculata, and from the brachium of the superior colliculus. The tracts wind round the crura cerebri (cerebral peduncles) and join the optic chiasma. In the chiasma the medial fibres decussate with the corresponding fibres of the opposite tract, while the lateral fibres pass on to the eyeball of the same side.
This commissure lies on the inferior surface of the floor of the third ventricle, and is lodged in a groove immediately in front of the olivary eminence. In the posterior part of the chiasma will be found a bundle of fibres linking up the optic tracts, the commissure of Guclden.
These nerves pierce the dura mater to enter the orbit through the optic foramen. Each is accompanied by the ophthalmic artery. Directed forwards and laterally the nerve runs beneath the superior rectus muscle. Here it is crossed obliquely by the nasal (naso-ciliary) nerve and the ophthalmic artery, and is surrounded by the ciliary nerves and vessels. It penetrates the eyeball one-eighth of an inch on the medial side of the antero-posterior axis, and having passed through the sclerotic and choroid coats, spreads out to form the inner layer of the retina. The arteria centralis retinae lies in the substance of the nerve.