2. The group of four muscles which make up the abdominal wall consists of:
- The external oblique (the most superficial of the four, a muscle from the fifth to twelfth ribs) whose fibers are directed downward and medially from the lower ribs to the linea alba (a fibrous band) and pelvis.
- The internal oblique (a slanting, small, thin, deep muscle of the abdomen), whose fibers are directed upward and medially from the iliac crest (hip bone) and lumbodorsal fascia (loose tissue) to the lower ribs.
- The rectus abdominis, a vertically oriented muscle from the crest of the pubis (pelvis) to the cartilages of the fifth, sixth, and seventh ribs and xiphoid process.
- The transversus abdominis, whose fibers are oriented transversely (sideways or at an angle across something).
These muscles participate in a variety of functions, including flexion, side bending and rotation of the trunk, stabilization of the trunk in the upright posture, the expiratory phase of respiration, coughing, and Valsalva's maneuver.
The term "Valsalva's maneuver" is a maneuver in which the patient holds his or her breath or gives a voluntary cough or sneeze to produce pain.
These activities of holding the breath, coughing, or sneezing increase the pressure of the cerebrospinal fluid which enlarges the pressure against the already pressured nerve, causing pain and numbness. The location of this intensified pain also contributes to the medical diagnosis.