Lateral perspective of the mid-basilar artery and prepontine cistern. For orientation, the left side of this image is rostral and the top of this image is ventral (the dura covering the clivus). The AICA is the largest branch of the basilar artery and, during its anterior pontine segment, has a close relationship with the abducens nerve which arises from the pontomedullary junction and courses rostrally over the clivus. Other branches of the mid basilar artery include circumflex pontine perforating arteries, which nourish the pons. The transverse pontine vein is the major vein of the ventral pons and lies in close proximity to the trigeminal nerves. (Image courtesy of AL Rhoton, Jr.)