Using a customer supplied envelope, an individual can mail a Priority Mail Express letter envelope weighing one ounce up to sixteen ounces for $31.20 plus the extra fee of $12.50 to add Sunday/Holiday Delivery.
muscle cell-an elongated contractile cell that forms the muscles of the body. muscle fiber, muscle fibre. fibre, fiber-any of several elongated, threadlike cells (especially a muscle fiber or a nerve fiber).
For other uses, see Muscle (disambiguation). Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and motion.