Which word means most nearly the same as the underlined word in this sentence?
During the bypass surgery, the surgeon had to locate the anterior veins first before she could reach the heart itself.

The word anterior comes from the Latin ante, meaning before or nearer to the front, so frontal would be the best answer. Posterior comes from post or behind. Aft is “in the rear” or at the end, and exterior means “outside of something.” While the veins the surgeon is locating are outside of the heart, anterior and frontal are closer in meaning in this context.