Human Anatomy - Kotsan I. Y. 2009

Muscles and Fascia of the Trunk
Muscles of the Anterior Abdominal Wall

The Muscles forming the anterior abdominal wall include the rectus abdominis and pyramidalis muscles (Fig. 100, 101, 103).

The rectus abdominis (m. rectus abdominis) is a paired, flat Muscle located on either side of the linea alba. It originates from the outer surface of the cartilages of Ribs V–VII and the xiphoid process of the Sternum. Extending downwards, the muscle narrows slightly and inserts onto the pubic crest (some authors, conversely, consider the pubic crest as the origin and the cartilages of ribs V–VII and the xiphoid process as the insertion). Along its length, the muscle is intersected by 3–4 tendinous intersections. One intersection is located at the level of the umbilicus, two are above the umbilicus, and one inconstant intersection is below the umbilicus. Function: flexes the trunk, participates in forming the abdominal press, pulls the Thorax downwards and lowers the ribs to assist in expiration, and elevates the pelvis when the thorax is fixed.

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Fig. 103. Muscles of the Trunk (lateral view).

A — superficial layer, B — pectoralis major and external oblique muscles removed, C — pectoralis minor and internal oblique muscles removed

A: 1 — pectoralis major, 2 — latissimus dorsi, 3 — aponeurosis of the external oblique muscle, 4 — iliac crest, 5 — external oblique muscle; B: 1 — serratus anterior, 2 — pectoralis minor, 3 — external intercostal muscles, 4 — anterior wall of the rectus sheath, 5 — internal oblique muscle, 6 — iliac crest, 7 — latissimus dorsi; C: 1 — medial border of the scapula, 2 — serratus anterior, 3 — internal intercostal muscles, 4 — pyramidalis muscle, 5 — rectus abdominis, 6 — transversus abdominis, 7 — posterior wall of the rectus sheath, 8 — external intercostal muscles

Innervation: intercostal nerves, iliohypogastric and ilioinguinal nerves.

The pyramidalis muscle (m. pyramidalis) is a small, variable in size, triangular muscle. It originates from the pubic crest. The muscle fibers converge as they ascend and insert at various levels of the lower PARTS OF THE linea alba. Function: tightens the linea alba.

Innervation: intercostal nerves, iliohypogastric and ilioinguinal nerves.