Vertebral arteries, circle of Willis, shown in isolation with vertebrae and skull, in 4 numbered illustrations. 2 illustrations of cervical spine and occipital bone shown with vertebral arteries, posterior and lateral views. 1 illustration of atlas with basilar artery, posterior view. 1 illustration of the base of skull, divided in transverse section to show cranial fossa, circle of Willis, middle cerebral artery shown, superior view.