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Rectus Sheath Anatomy

The rectus sheath is the strong, incomplete fibrous compartment of the rectus abdominis and pyramidalis muscles. Also found in the rectus sheath are the superior and inferior epigastric arteries and veins, lymphatic vessels, and distal portions of the thoraco-abdominal nerves (abdominal portions of the anterior rami of spinal nerves T7–T12).

Rectus Sheath Anatomy

The rectus sheath is formed by the decussation and interweaving of the aponeuroses of the flat abdominal muscles. The external oblique aponeurosis contributes to the anterior wall of the sheath throughout its length. The superior two thirds of the internal oblique aponeurosis splits into two layers (laminae) at the lateral border of the rectus abdominis; one lamina passing anterior to the muscle and the other passing posterior to it. The anterior lamina joins the aponeurosis of the external oblique to form the anterior layer of the rectus sheath. The posterior lamina joins the aponeurosis of the transversus abdominis to form the posterior layer of the rectus sheath.

See Also: Abdominal Rectus Muscle

Beginning approximately one third of the distance from the umbilicus to the pubic crest, the aponeuroses of the three flat muscles pass anterior to the rectus abdominis to form the anterior layer of the rectus sheath, leaving only the relatively thin transversalis fascia to cover the rectus abdominis posteriorly.

A crescentic arcuate line demarcates the transition between the aponeurotic posterior wall of the sheath covering the superior three quarters of the rectus and the transversalis fascia covering the inferior quarter. Throughout the length of the sheath, the fibers of the anterior and posterior layers of the sheath interlace in the anterior median line to form the complex linea alba.

Rectus Sheath

The posterior layer of the rectus sheath is also deficient superior to the costal margin because the transversus abdominis is continued superiorly as the transversus thoracis, which lies internal to the costal cartilages, and the internal oblique attaches to the costal margin. Hence, superior to the costal margin, the rectus abdominis lies directly on the thoracic wal.

The linea alba, running vertically the length of the anterior abdominal wall and separating the bilateral rectus sheaths, narrows inferior to the umbilicus to the width of the pubic symphysis and widens superiorly to the width of the xiphoid process. The linea alba transmits small vessels and nerves to the skin. In thin muscular people, a groove is visible in the skin overlying the linea alba.

At its middle, underlying the umbilicus, the linea alba contains the umbilical ring, a defect in the linea alba through which the fetal umbilical vessels passed to and from the umbilical cord and placenta. All layers of the anterolateral abdominal wall fuse at the umbilicus. As fat accumulates in the subcutaneous tissue postnatally, the skin becomes raised around the umbilical ring and the umbilicus becomes depressed. This occurs 7–14 days after birth, when the atrophic umbilical cord “falls off.”

References & More

  1. Sevensma KE, Leavitt L, Pihl KD. Anatomy, Abdomen and Pelvis, Rectus Sheath. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537153/
  2. Clinically Oriented Anatomy – 8th Edition
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