Rectus sheath

The rectus sheath is formed by the aponeuroses of the transversus abdominis and the external and internal oblique muscles. It contains the rectus abdominis and pyramidalis muscles.

It 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:

Within the sheath, the layers vary:

Below the sheath are the following three layers:

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