|Derivation||The straight (rectus) muscle of the abdomen.|
|Origin||The pubic arch of the pelvis.|
|Insertion||Inferior end of the sternum and cartilage of ribs #5-7.|
|Action||Bends ribcage forward toward hips, and vice-versa.|
Rectus abdominis is a thick sheet of muscle covering the front of the torso from the ribs to the pelvis, and is responsible for pulling the two toward each other, bending the spine at the lower back.
It is divided into distinct segments by tendonous lines, three horizontal and three vertical. A vertical line called the linea alba (
white line) runs down the middle of the muscle to the navel. The lateral sides of the muscle are bordered by a groove that separates it from the mass of external oblique.
The three horizontal lines (referred to as the transverse lines) give the muscle its distinctive
The first transverse line creates a rounded shape under what would otherwise be an angular hollow below the sternum where the ribs meet. The thoracic arch is pointed in the Gothic style, but the first transverse line seems to carry the thoracic arch through a lower point, forming a round Romanesque arch.
The second and third transverse lines vary greatly in position, shape, and symmetry. General rule would put the second line around the level of the tenth rib, and the third line in the middle of the fist-high space between the last rib and the pelvis. (The navel is somewhere around the third line, usually on or below.)
The degree of arch in the transverse lines decreases from top to bottom, but this too can vary.