abnormal basilar artery morphology dilated basilar artery MP:0013187 MPheno.ontology stretched or widened aperture of the luminal space of the unpaired artery that is formed by the union of the two vertebral arteries, runs forward within the skull just under the pons, divides into the two posterior cerebral arteries, and supplies the pons, cerebellum, posterior part of the cerebrum, and the inner ear