The rectus abdominis muscle, () also known as the "abdominal muscle" or simply the "abs", is a paired straight muscle. It is a paired muscle, separated by a midline band of connective tissue called the linea alba. It extends from the pubic symphysis, pubic crest and pubic tubercle inferiorly, to the xiphoid process and costal cartilages of ribs V to VII superiorly. The proximal attachments are the pubic crest and the pubic symphysis. It attaches distally at the costal cartilages of ribs 5-7 and the xiphoid process of the sternum. The rectus abdominis muscle is contained in the rectus sheath, which consists of the aponeuroses of the lateral abdominal muscles. The outer, most lateral line, defining the rectus is the linea semilunaris. Bands of connective tissue traverse the rectus abdominis, separating it into distinct muscle bellies. In the abdomens of people with low body fat, these muscle bellies can be viewed externally. They can appear in sets of as few as two to as many as twelve, although, six is the most common. Structure The rectus abdominis is a very long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba. Tendinous intersections (intersectiones tendineae) further subdivide each rectus abdominis muscle into a series of smaller muscle bellies. Tensing of the rectus abdominis causes the muscle to expand between each tendinous intersection. The upper portion, attached principally to the cartilage of the fifth rib, usually has some fibers of insertion into the anterior extremity of the rib itself. Size It is typically around 10 mm thick., although, some athletes can have a rectus up to 20 mm thick. Typical volume is around 300 cm³ in non-active individuals and 500 cm³ in athletes. Blood supply The rectus abdominis has many sources of arterial blood supply. Classification of the vascular anatomy of muscles: First, the inferior epigastric artery and vein (or veins) run superiorly on the posterior surface of the rectus abdominis, enter the rectus fascia at the arcuate line, and serve the lower part of the muscle. Second, the superior epigastric artery, a terminal branch of the internal thoracic artery, supplies blood to the upper portion. Finally, numerous small segmental contributions come from the lower six intercostal arteries as well. Nerve supply The muscles are innervated by thoraco-abdominal nerves, these are continuations of