serratus posterior superior muscle serratus posterior superior muscle the serratus posterior superior muscle is a thin, quadrilateral muscle. it is situated at the upper back part of the thorax, deep to the rhomboid muscles. serratus posterior superior musclethin film-like object, at center, is serratus posterior superior muscle.detailsoriginnuchal ligament (or ligamentum nuchae) and the spinous processes of the vertebrae c7 through t3insertionthe upper borders of the 2nd through 5th ribsarteryintercostal arteriesnerve2nd through 5th intercostal nervesactionselevates ribs 2-5 identifierslatinmusculus serratus posterior superiorta98a04.3.01.011ta22236fma13401anatomical terms of muscle structure the serratus posterior superior muscle arises by an aponeurosis from the lower part of the nuchal ligament, from the spinous processes of c7, t1, t2, and sometimes t3, and from the supraspinal ligament. it is inserted, by four fleshy digitations into the upper borders of the second, third, fourth, and fifth ribs past the angle of the rib. function the serratus posterior superior muscle elevates the second to fifth ribs. this aids deep respiration. additional images position of serratus posterior superior muscle (shown in red). serratus posterior superior muscles are labeled at center left and center right.