Human Anatomy - Kotsan I. Ya. 2009

Muscles and fasciae of the trunk
Sheath of the rectus abdominis muscle

Each of the rectus abdominis Muscles is enclosed within a sheath formed by the broad aponeuroses of the lateral Abdominal muscles. The sheath of the rectus abdominis Muscle (Vagina m. recti abdominis) has anterior and posterior walls. The upper two-thirds of the anterior wall are formed exclusively by the aponeurosis of the external oblique muscle and the anterior lamina of the aponeurosis of the internal oblique muscle, which splits near the lateral margin of the rectus muscle into two laminae: anterior and posterior. The posterior wall of the rectus sheath is formed by the aponeurosis of the transversus abdominis muscle and the posterior lamina of the aponeurosis of the internal oblique muscle. In the lower third, the aponeuroses of the oblique and transverse abdominal muscles pass anterior to the rectus muscle, forming the anterior wall of the sheath. Consequently, in its lower third, the rectus sheath lacks a posterior wall, save for the transversalis fascia, which covers the posterior surface of the muscle in this region.

The anterior wall of the sheath is firmly adherent to the tendinous intersections of the rectus abdominis muscle. The posterior wall of the sheath exhibits no such attachments.

The Functional Significance of the rectus sheath lies in its ability to secure THE POSITION OF this muscle, providing a flexible framework for it. Together with the linea alba, it serves as a site of fixation where the Muscles of the right and left sides of the abdomen anchor relative to one another. This establishes optimal conditions for the maximal participation of the abdominal muscles in trunk movements, particularly in flexion and lateral bending. Furthermore, the rectus sheath contributes to the reinforcement of the anterior abdominal wall.