Which prefix signifies movement towards the inside?

The prefix that signifies movement towards the inside is "en-." This prefix is derived from the Latin preposition meaning "in" or "into." In medical terminology, it is often used to describe processes, conditions, or actions that involve entering into or being contained within a particular area or structure. For example, "enclose" means to surround or contain something entirely within a boundary.

Other prefixes such as "epi-" refer to something that is upon or over, "circum-" relates to being around something, and "di-" denotes separation or movement apart rather than inward. Therefore, "en-" is the appropriate choice for indicating movement towards the inside.