circle of Willis - a ring of arteries at the base of the brain

arteria communicans, communicating artery - any of three arteries in the brain that make up the circle of Willis

neural structure - a structure that is part of the nervous system

brain cell - a nerve cell in the brain

central nervous system, CNS, systema nervosum centrale - the portion of the vertebrate nervous system consisting of the brain and spinal cord

neencephalon, neoencephalon - the part of the brain having the most recent phylogenetic origin; the cerebral cortex and related parts

forebrain, prosencephalon - the anterior portion of the brain; the part of the brain that develops from the anterior part of the neural tube

mesencephalon, midbrain - the middle portion of the brain

hindbrain, rhombencephalon - the posterior portion of the brain including cerebellum and brainstem

brain stem, brain-stem, brainstem - the part of the brain continuous with the spinal cord and comprising the medulla oblongata and pons and midbrain and parts of the hypothalamus

ventricle - one of four connected cavities in the brain; is continuous with the central canal of the spinal cord and contains cerebrospinal fluid

head, caput - the upper part of the human body or the front part of the body in animals; contains the face and brains; "he stuck his head out the window"