Veebral aery is one of the principal aeries which supply the brain. It arises from the posterosuperior aspect of the first pa of the subclan aery near its commencement. The first pa extends from the origin of the aery (from the subclan aery) to the transverse process of the sixth cervical veebra. 2nd pa runs through the foramen transversarium of the upper six cervical veebrae. 3rd pa lies in the occipital triangle. 4th pa extends from the posterior atlantooccipital membrane to the lower border of the pons. "It passes medially above the posterior arch of the atlas and then ascends through foramen magnum into the skull".