Epimysium

Epimysium is a dense irregular connective tissue sheath that surrounds an entire skeletal muscle. It lies just beneath the muscle's outer fascia and is the outermost layer of connective tissue in the muscle organ, continuous with the connective tissue of tendons and with the deep fascia. The epimysium encloses the muscle as a single functional unit and, where present, blends with the tendon at the muscle-tendon junction. The layer is connected to the perimysium at the muscle's surface and contributes to the transmission of force from muscle to tendon. The epimysium contains blood vessels, nerves, and lymphatics that service the muscle, and provides pathways for these structures to reach the deeper muscle tissue. The epimysium is mainly composed of dense irregular collagen fibers (predominantly type I, with type III), organized to resist stresses from multiple directions.

Functionally, the epimysium supports the muscle by maintaining its shape, distributing tension across the muscle, and protecting inner fascicles. It also helps contain the muscle's vascular and neural networks and can influence the mechanical interaction between muscles and surrounding tissues via the fascia. In clinical context, injuries such as strains may disrupt the epimysium or its attachments, affecting force transmission and leading to pain or restricted movement. The epimysium is continuous with the tendinous attachments and with the surrounding deep fascia, reflecting its integrated role in muscle mechanics and structural organization.