The eighth nerve, auditory, lies beneath the lower margin of the middle peduncle of the cerebellum, between the seventh nerve and the flocculus. It divides behind into two roots, an anterior and posterior, which embrace the restiform body. The anterior root, in conjunction with the seventh nerve, passes through the restiform triangle, occupying its superior angle, to reach the floor of the fourth ventricle, where it joins the posterior tract of the fillet, and passes downward on the inner side of the restiform body, to reach the auditory nucleus. The posterior root passes inward beneath the arch of the restiform body, and across it to the floor of the fourth ventricle, upon which it forms the inferior striae transvers. This root divides into striae, which are lost in the raphe, and is connected with the arciform fibres, and the commissure of the flocculus. It is probable that the roots of the auditory nerve have the same disposition as those of the olfactory and the optic nerves, and possibly this arrangement is common to the roots of all the sensory nerves.
The ninth nerve, glosso-pharingeal, lies beneath the floc culus above the pnemuogastric nerve, and passes inward behind the olive to the floor of the fourth ventricle, where it is connected with its nucleus.
The tenth nerve, or pueumogastric, is beneath the ninth, passes inward behind the olive to the floor of the fourth ven tricle. Its nucleus is connected with the upper part of the olive by a commissure.
The eleventh nerve, spinal accessory, arises by slips from the lateral tract of the spinal cord as low as the sixth or seventh cervical vertibrpe, and front the side of the medulla, which unite into a trunk that lies behind the flocculus and the pneuntogastric nerve. Its deep origin is from the anterior horns of the grey matter of the cord.
The twelfth nerve, hypoglossal, arises from between the olive and anterior pyramid of the medulla. Its roots pass backward between the olive and the fundamental root zone to the floor of the fourth ventricle. Its nucleus is connected with the lower part of the olive aud with the opposite anterior pyramid.