Penetrating branches of the Circle of Willis.  Coronal section through the brain at the level of the optic chiasm and bifurcation of the internal carotid artery (ICA).  On the left side of image, the ICA bifurcates into its two terminal branches, the anterior cerebral artery (ACA) and middle cerebral artery (MCA).  The ACA runs medially above the optic nerve and chiasm and is joined at the midline to the opposite ACA via the anterior communicating artery.  The proximal portion of the ACA gives origin to the recurrent artery of Heubner, or medial striate artery.  The latter artery supplies the anteromedial basal ganglia (head of caudate, rostral putamen, and nucleus accumbens), in addition to the anterior and inferior portions of the anterior limb of the internal capsule.  The ACA then enters the interhemispheric fissure to supply the orbital and medial surfaces of the frontal lobes.  The MCA is larger than the ACA and is regarded as the direct continuation of the ICA.  The MCA travels laterally to enter the lateral fissure of Sylvius.  Along its course, the MCA gives off several lateral striatal (or lenticulostriatal) arteries.  The latter are narrow, vertically-oriented vessels that penetrate the brain near their point of origin and supply deep structures of the diencephalon and telencephalon, including the head and body of the caudate nucleus, lenticular nucleus, and both the anterior limb (seen in this image) and posterior limb (not visible here) of the internal capsule. (Image courtesy of AL Rhoton, Jr.)