The fourth pair supply the superior obliques, and the sixth the external
recti; so that III., IV., and VI. are alike purely motor nerves, small and
distributed, to the orbit. The fifth nerve, the trigeminal, is a much
larger and more important one; it is a mixed nerve, having three main
branches, of which the first two are chiefly sensory, the third almost
entirely motor; it lies deeply in the orbit. V1 (see Sheet 9) runs up
over the recti behind the eyeball, it is the ophthalmic branch; V2, the
maxillary branch, runs deeply under the eyeball and emerges in front
of the malar, and V3, the mandibular branch, runs down on the inner
side of the jaw-bone to the jaw muscles and tongue.