Ans. a. Abducent nerve (Ref: Gray's anatomy 40/e p240; Netter Collection of Medical Illustrations 2013/Vol. 7/e p178) Abducent nerve nucleus is located deep to facial colliculus."Facial colliculus is situated in the pons. It overlies the abducent nucleus. The facial nerve originates from its nucleus and goes around the abducent nerve. This is called as neurobiotaxis. "---Gray s anatomy 40/e p240"On each side of the median sulcus is a longitudinal elevation, the medial eminence. lateral to which lies sulcus limitans. Its superior part is the locus ceruleus, coloured bluish-grey from the patch of deeply pigmented nerve cells. Also lateral to the upper part of the medial eminence is a slight depression, the superior fovea, and just below and medial in this fovea is a rounded swelling, the facial colliculus, which overlies the nucleus of the abducens (VI) nerve and the facial (VII) nerve fibers encircling in the motor nucleus of the facial nerve lies more deeply in the pons. Inferolateral to the superior fovea is the upper part of the vestibular area, which overlies parts of the nuclei of the vestibulococchlear (VIII) nerve. " Netter Collection of Medical Illustrations 2013/Vol. 7/e p178