Position prefixes answer one question: where. Endo- is within, epi- is upon, peri- is around, sub- is beneath, inter- is between two things and intra- is inside one. Click any layer, space or arrow on the cross-section to see which prefix owns it — then switch to Find the site and let a clinical order send you there.
Schematic, not to scale. Rings of the heart wall, working outward from the blood: blood, lining, muscle, outer membrane, space, sac. Every ring but one is named by its prefix.
The prefix that owns that place
Position prefixes not drawn here
circum- aroundsupra- aboveinfra- belowecto-, ec- outsidemeso- middlejuxta- adjoiningmeta- beyondipsi- same sidecontra- opposite sidedia- through, completeana- up, apartcata- downex-, exo- outante- in front ofpost- behind
Per- versus peri-. A percutaneous procedure passes through the skin; a pericardial effusion sits around the heart. The i is the whole difference.