The _olfactory nerve_. The anterior surface of the olfactory lobe fills a large foramen in the anterior wall of the cranium and is pressed closely against the posterior surface of the nasal sac. Numerous small nerves, collectively forming the olfactory nerve, arise from the anterior face of the lobe, penetrate the membraneous wall of the olfactory organ, and are distributed to its highly folded surface.
The _terminal nerve, Nervus terminalis_, is a slender nerve running along the medial surface of the stalk of the olfactory lobe. Follow it backward to its origin on the anterior surface of the cerebral hemisphere, deep in the median fissure (in Eugaleus on the ventral surface). Trace it forward over the dorsal surface of the olfactory lobe to where it enters the nasal sac. The terminal nerve is a true cranial nerve which has escaped notice until recent years. It is associated with the olfactory nerve in vertebrates generally from fishes to men. The fibres of the terminal nerve remain distinct from those of the olfactory nerve, both in the olfactory organ and in the brain. Its function is unknown. There is still a division of opinion among authorities as to whether the terminal nerve should be considered to be a distinct cranial nerve, or a portion of the olfactory nerve.
The _optic nerve_ can be seen at the bottom of the orbit between the eye and the skull, nearly under the superior oblique muscle. It arises from the ventral side of the diencephalon, passes outward, penetrates the orbit at its infero-medial angle, and continues directly outward to the eyeball.
The _trochlear nerve_, or _patheticus_, penetrates the wall of the orbit opposite the optic lobe. Follow it back to its origin from the dorsal surface of the brain in the depression between the optic lobes and the cerebellum. Then follow it from the skull to the superior oblique muscle, which it innervates.
The _oculo-motor nerve_ arises from the ventral surface of the midbrain, passes outward, and penetrates the orbit on a level with and just anterior to the origins of the recti muscles. It divides immediately into three parts; two pass to the anterior and superior recti respectively, while the third passes downward along the posterior surface of the eyeball to the inferior rectus and inferior oblique muscles. In tracing this nerve the palatine process of the upper jaw will be seen projecting from below into the orbit.