The course of the Vertebral artery is considered in four segments. The first part arises from the subclavian and extends to the transverse foramen of C6. The second part ascends almost vertically through the transverse foramina of C6 – C2. At this level the vertebral artery lies anterior to the emerging cervical spinal nerves. The third part lies in the suboccipital triangle and the vertebral canal below the inferior border of the posterior atlanto-occipital membrane. The fourth part pierces the dura and arachnoid mater inclining anterior to the medulla and uniting with its fellow to form the basilar artery at the lower pontine border.