I and II. The olfactory and optic nerves. These two large nerves go immediately to their respective sense organs, so that no further discussion of them need be here given. III. The oculomotor nerve. The single stem divides into three branches: a median, going to the externus rectus muscle; a lateral, going to the inferior rectus muscle; and an intermedial, going to the inferior oblique muscle. IV. The trochlear (pathetic) nerve leads to the superior oblique muscle. V. The trigeminal nerve. The distribution of this nerve is very complicated. It has three main divisions: (1) the ophthalmic branch, (2) the superior maxillary branch, and (3) the inferior maxillary branch. (1) The ophthalmic in turn divides into two branches: the smaller, frontal, going to the integument of the upper and lower eyelids; the larger, nasal, going chiefly to the nasal cavity but also sending some small branches to the upper and lower eyelids. (2) The superior maxillary branch separates into a number of divisions: (a) a branch that, in the neighborhood of the auditory capsule, fuses with the facial nerve; (b) a twig to the integument of the forehead and to the upper and lower eyelids; (c) a branch to the Harderian gland and the conjunctiva; (d) a branch to the neighborhood of the cheek, to the angle of the mouth, and to the palatine branch of the facial nerve; (e) a branch to the palate; (f) a branch to the integument of the upper jaw; (g) a branch to the teeth of the upper jaw. (3) The inferior maxillary branch divides into four branches: (a) this division supplies the skin of the cheek region; (b) a branch to the chewing muscles; (c) a branch that divides into two nerves--the first going to the skin of the lower jaw, the second dividing again into two nerves, both of which lead to the integument of the lower jaw; (d) the fourth division of the inferior maxillary, known as the inferior alveolar, itself divides into two twigs--(a′) the first twig divides into two parts, a larger and a smaller, both of which lead, by different paths, to the inner skin of the mouth; (b′) the second twig divides into four parts--two leading to the mylohyoid muscle and to the integument at the corner of the mouth, one to the integumental glands at the corner of the mouth, and one to the floor of the mouth cavity. VI. The abducens nerve leads to the retractor oculi muscle and to the muscle for the nictitating membrane. VII. The facial nerve gives off three main branches: (1) the first divides again into three twigs--(a) connecting with a branch of the trigeminal nerve, (b) and (c) connecting with the trigeminal and also leading to the palate; (2) the second branch divides into two twigs that connect with the glossopharyngeal nerve; (3) the third branch divides into two parts, a muscular twig, and the chorda tympani. VIII. The auditory or acoustic nerve leads, of course, to the sensory regions of the ear.