endomysium

This term is a specialized anatomical descriptor used primarily in histology and kinesiology. It describes the innermost layer of the connective tissue hierarchy in skeletal muscle, distinguishing it from the perimysium (which wraps bundles of fibers) and the epimysium (which wraps the entire muscle).

As a technical biological term, it is typically treated as an uncountable noun in clinical descriptions when referring to the tissue type generally. However, it can be used as a countable noun when referring to the specific layer surrounding a single fiber.