A 45-year-old male presents to the outpatient clinic for routine blood pressure monitoring. The physician places the blood pressure cuff over the arm and auscultates with a stethoscope over the cubital fossa. The structure marked **B** in the diagram is the site where Korotkoff sounds are heard during this measurement. Which of the following best describes the anatomical relationship of this structure to the surrounding contents of the cubital fossa?