Anatomical segments

P1: PCA from the origin to posterior communicating artery (AKA mesencephalic, precommunicating, circular, peduncular, basilar...). The long and short circumflex and thalamoperforating arteries arise from P1
P2: PCA from origin of PComA to the origin of inferior temporal arteries (AKA ambient, post-communicating, perimesencephalic), P2 traverses the ambient cistern, hippocampal, anterior temporal, peduncular perforating, and medial posterior choroidal arteries arise from P2
P3: PCA from the origin of the inferior temporal branches to the origin of the terminal branches (AKA quadrigeminal segment). P3 traverses the quadrigeminal cistern
P4: segment after the origin of the parieto-occipital and calcarine arteries, includes the cortical branches of the PCA

P1 segment

P1 Segment	Feature
Posterior thalamoperforator arteries	From the basilar artery and P1, travels through the posterior perforated substance behind the mamillary bodies Supply: thalamus, hypothalamus, subthalamus, and midbrain (cranial nerves III and IV)
Medial posterior choroidal arteries	Travels anteromedially along the roof of the third ventricle Supply: midbrain tectum, posterior thalamus, pineal gland, and tela choroidae of the third ventricle
Meningeal branches	Supply: tentorium and the falx