The only cranial nerve to emerge from dorsal aspect of brainstem is

.Surface attachment. Trochlear nerve is attached to the superior medullary velum one on each side of the frenulum veil just below the inferior colliculus. It is the only cranial nerve which emerges on the dorsal aspect of the brainstem. Ref : B D Chaurasia's Human Anatomy, sixth edition, volume 3 , pg. no. 364 Ref : B D Chaurasia's Human Anatomy, sixth edition, volume 3 , pg. no. 364 ( fig . 24. 1 )