Myoseptum

a wall of connective tissue that separates the myomeres in lancelets, vertebrate animals, and humans. The myosepta stretch between the axial skeleton and the skin, thus supporting the muscle fibers of the myomeres. (Fish have muscle ossicles in the myosepta.) Fish and amphibians also have a horizontal myoseptum that divides the myomeres into dorsal and ventral sections. In tailless amphibians and in the Amniota (with the exception of snakes and lizards), myosepta are present only in the embryonic stage. In man, the vestiges of myosepta are the connective-tissue walls of the rectus abdominis.