The prefix 'INNER' is used to describe something that is located WITHIN or INSIDE of something else. Endo- is a prefix derived from the Greek word for 'WITHIN', and is used to describe something that is located INSIDE of a body or organ. EsO- is a prefix derived from the Greek word for 'OUTSIDE', and is used to describe something that is located OUTSIDE of a body or organ. ENTO- is a prefix derived from the Greek word for 'INSIDE', and is used to describe something that is located INSIDE of a structure or container. Ent- is a prefix derived from the Greek word for 'OUTSIDE', and is used to describe something that is located OUTSIDE of a structure or container.