rectus sheath rectus sheath the rectus sheath, also called the rectus fascia, is formed by the aponeuroses of the transverse abdominal and the internal and external oblique muscles. it contains the rectus abdominis and pyramidalis muscles. rectus sheathdetailsidentifierslatinvagina musculi recti abdominista98a04.5.01.003ta22359fma9587anatomical terminology structure the rectus sheath can be divided into anterior and posterior laminae. the arrangement of the layers has important variations at different locations in the body. below the costal margin for context, above the sheath are the following two layers: camper's fascia (anterior part of superficial fascia) scarpa's fascia (posterior part of the superficial fascia) within the sheath, the layers vary: regionillustrationdescription above the arcuate lineat the lateral margin of the rectus, the aponeurosis of the internal oblique divides into two lamellae: one of which passes in front of the rectus, blending with the aponeurosis of the external oblique as well as the aponeurosis of the anterior half of the internal oblique. the other, behind it, blending with the aponeurosis of the transversus as well as the posterior half of the internal oblique, and these, joining again at the medial border of the rectus, are inserted into the linea alba. below the arcuate linebelow this level, the aponeuroses of all three muscles (including the transversus) pass in front of the rectus. below the sheath are the following three layers: transversalis fascia extraperitoneal fat parietal peritoneum the rectus, in the situation where its sheath is deficient below, is separated from the peritoneum only by the transversalis fascia, in contrast to the upper layers, where part of the internal oblique also runs beneath the rectus. because of the thinner layers below, this region is more susceptible to herniation. above the costal margin since the tendons of the internal oblique and transversus abdominis only reach as high as the costal margin, it follows that above this level the sheath of the rectus is deficient behind, the muscle resting directly on the cartilages of the ribs, and being covered only by the tendons of the external obliques. clinical significance the rectus sheath is a useful attachment for surgical meshes during abdominal surgery. this has a higher risk of infection than many other attachment sites. additional images the cremaster the interfoveolar ligament, seen from in front.