These narrow, initially unbranched, arteries are emitted as a bundle from the anterior part of
the basal artery and from the first part
of the posterior cerebrum artery . The vascular bundle penetrates the
midbrain (mesencephalon) via the posterior
vascular inlet (substantia perforata posterior) at the bottom of the
cerebral arm pit (fossa interpeduncularis) and supplies the interior of the mesencephalon, the
subthalamus area and the posterior parts of the
thalamus.