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The rectus abdominis muscle or musculus rectus abdominis in Latin (‘rectus’ meaning straight) is one of the two vertical muscles belonging to the anterior wall of the abdomen (the other being the pyramidalis muscle). It is a long strap-like paired muscle, separated in the midline by a tendinous raphe, the linea alba. It is mostly enclosed by a fibrous aponeurotic rectus sheath, and has a broad and thin superior and a narrow and thick inferior.
The muscle fibers of the rectus abdominis muscle are interrupted by three transverse fibrous bands or tendinous intersections. They mostly extend halfway along the body of the muscle, and tend to fuse with the fibers of the anterior lamina of the rectus sheath. They can be easily seen on muscular individuals with well-developed rectus abdominis.
The rectus abdominis originates from two tendons. The large lateral tendon is attached to the pubic crest and may extend past the pubic tubercle to the pectineal line. While the medial tendon merges with the contralateral muscle fibers and into the ligamentous fibers covering the symphysis pubis. Some fibers may rise from the inferior aspect of the linea alba as well. The rectus muscle attaches superiorly through three slips of muscles to the 5th, 6th, and 7th costal cartilages. It may extend to the 3rd and 4th ribs if the slip of the most lateral fibers is absent. The medial fibers are usually inserted to the side of the xiphoid process. This muscle can be palpated by asking the patient to raise their head and shoulders against resistance.
The main vascular supply of the rectus abdominis muscle is provided by the superior epigastric artery (arising from the internal thoracic artery), and the inferior epigastric artery (arising from the external iliac artery). The latter being the larger of the two. It may also receive contributions from the small terminal branches of the lower three posterior intercostal arteries, the subcostal artery, the posterior lumbar arteries and the deep circumflex artery.
The rectus muscle has a powerful vertebral column flexion function. It also compresses the abdominal content and maintains the tone of the abdominal wall during straining. It is innervated by the ventral rami of the lower seven thoracic nerves (T7 to T12).
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