A 45-year-old man is brought to the emergency department in cardiac arrest. The trauma team decides to establish emergency central venous access via the femoral approach. During the procedure, the physician palpates the femoral pulse and attempts to cannulate the artery. However, the needle is inadvertently placed medial to the intended target. The structure marked **C** in the diagram is now at risk of puncture. Which of the following best describes the anatomical relationship that explains this complication?