The internal abdominal oblique muscle lies on the sides and front of the abdomen and is the intermediate of the three flat muscles in this area, below the external oblique and above the transverse abdominal muscle. It is broad, thin and irregularly four-sided and occupies the lateral walls of the abdomen, stretching across to the front. Both sides, acting together, flex the vertebral column by drawing the pubis toward the xiphoid process (the smallest of the three parts of the breastbone). One side also bends the vertebral column sideways and rotates it, bringing the shoulder of that side forward. The external abdominal oblique muscle is also irregularly four-sided in form and lies superficial to the internal oblique muscle. Both sides, acting together, flex the vertebral column, drawing cartilage down toward the pubis. One side acts alone bending the vertebral column sideways, rotating it to bring the shoulder of the opposite side forward. Both of the abdominal oblique muscles work to compress abdominal contents, assist in the digestive process and in forced expiration.