Which artery is formed by joining of 2 vertebral arteries -

Ans. is 'd' i.e., Basilar artery o Basilar artery is formed by the union of tw o vertebral arteries at the lower border of pons. It lies in the median groove of pons in cistema pontis and at the upper border of pons by dividing into two posterior cerebral arteries,Vertebral ArteryIt arises from 1st part of subclavian arteryFirst Part : Origin to the foramen transversarium of C, vertebra. It lies in the scalenovertebral/vertebral triangle (triangle of vertebral artery) between scalemus anterior and longus colli muscles.Second Part: This part passes through foramina transversaria of upper 6 cervical vertebrae (C6 to C1).Third Part: It extends from foramen transversarium of C1. to foramen magnum, lying in a groove on the upper surface of posterior arch of atlas.This part of the artery lies in the suboccipital triangle. It then enters the vertebral canal by passing deep to the lower arched margin of posterior atlanto-occipital membrance.Fourth Part: It lies in the posterior cranial fossa extending from the foramen magnum to the lower border of pons.In the vertebral canal, it pierces the dura and arachnid and ascends in front of hypoglossal nerve roots. At the lowerborder of pons both vertebral arteries unite to form the basilar artery.Cervical branchesSpinal branches : Enter vertebral canal through intervertebral foramina and supply cervical segments of spinal cord, meninges, and vertebrae.Muscular branches : Supply suboccipital muscles.Cranial Branches :Meningeal : Supply meninges of posterior cranial fossaPosterior spinalAnterior spinalMedullaryPosterior inferior cerebellarBasilar artery : A single median vessel formed by the union of the two vertebral arteries at the lower border of pons, runs upw ard in front of the pons, embedded in the groove, to bifurc ate into two posterior cerebral arteries at the upper border of pons. Its branches are :Labyrinthineanterior inferior cerebellarPontineSuperior cerebellarPosterior cerebral