system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Which of the following are unpaired vessel in CNS--
assistant
The correct answer is  Basilar artery  is single unpaired vessel, it is formed by right and left vertebral arteries, at lower border of pons and ends at upper border of pons by dividing into right and left posterior cerebral arteries.