The occipital sinus.
D002102:Cadaver; D003388:Cranial Fossa, Posterior / Q000033:anatomy & histology; D003392:Cranial Sinuses / Q000002:abnormalities / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006801:Humans; D009777:Occipital Bone / Q000002:abnormalities / Q000033:anatomy & histology; D011859:Radiography; D012886:Skull / Q000033:anatomy & histology* / Q000000981:diagnostic imaging