The external obliques are responsible for rotating the trunk and pulling the chest downward to compress the abdominal cavity. They also provide support for the rotation of the spine. These muscles are some of the largest parts of the human trunk. They have a "V" shape that follows the pattern of putting one's hands into a pocket, according to About.com.
The obliques are the outermost of the abdominals. These large, flat muscles cover the sides of the trunk. A subcutaneous fat layer covers the obliques in most humans, especially females, which means they often are not visible. The obliques connect to the seven lower ribs. They contract to aid in breathing, causing the lungs to expel air. Certain motions require the external obliques to work with other muscles. These motions include flexing the spine and rotating the trunk in a direction opposite to that of the pelvis.
The subcostal and intercostal nerves connect these muscles to the brain. They play a vital role in the minor adjustments to the abdomen to maintain balance. As a result, injury to one of these muscles is often debilitating. Their blood supply comes from the intercostal arteries, the deep circumflex iliac artery and the iliolumbar artery.