FCA1-0135

A 68-year-old woman is a known case of acute myeloid leukaemia and was treated with chemotherapy as a child. She now presents in rhesus, and you are called in to attend this patient as it is getting difficult to gain vascular access in her arms. The medical registrar asks you to site a cannula during the arrest call as intraosseous access is delayed. The ITU SHO wants to assist you in performing a venous cutdown of one of the veins in her ankle that passes anterior to the medial malleolus. Which vessel is this?