External Oblique Muscle
The fleshy digitations are arranged in an oblique (sloped or slanting at an angle; especially: any of the thin flat muscles forming the middle and lower muscles of the abdominal cavity) or line which runs inferiorly and anteriorly, with the upper digitations being attached closely to the cartilages of the corresponding ribs.
The lowest external oblique is attached to the apex (the tip or point) of the cartilage of the last rib. While the intermediate ones are at some distance from their cartilages. The other insertions are the Iliac crest, Pubic tubercle, and Linea alba.
The aponeurosis (sinew; a white sheet of tissue by which certain muscles are attached to bones) of the external oblique muscle forms the inguinal ligament. The muscle also contributes to the inguinal (pertaining to the or situated in the groin or lowest lateral part of the abdominal cavity) canal. Just below and deep to the external oblique lies the internal oblique muscle.
The external oblique functions to pull the chest downward and compress the abdominal cavity, which increases the intra-abdominal pressure as in the valsalva maneuver. It has limited actions in both flexion and rotation of the vertebral column. One side of the obliques contracting can create lateral flexion. It contributes in compression of the abdomen. It is categorized as a muscle of the Abdomen, in the Muscles of the torso, Spine flexors, Spine lateral flexors, and in a category list of Spine rotators, too. It is a muscle that is used to perform sit-ups and crunches during exercise.