Inguinal ligament
http://www.unm.edu/~lkravitz/Article%20folder/abdominal.html The external oblique muscles are the outermost fibers of the trunk, and are located on each side of the rectus abdominis. Their upper and lateral attachments are to the lower eight ribs by tendinous insertions that interdigitate (interlock like the fingers of folded hands) with the serratus anterior muscle on the side of the rib cage. The lower and middle attachments of the external obliques are to the anterior crest of the pelvis (iliac crest) and the aponeurosis of the linea alba from the ribs to the crest of the pubis.
The external oblique muscle actually becomes the inguinal ligament #(Hay & Reid, 1982)#. The fibers of this muscle run diagonally, forming a “V” shape, similar to putting your hands into your coat pocket.
Beneath the external oblique muscles, running at approximately right angles to them, are the internal oblique muscles which form an inverted “V” shape. Their upper and medial attachments are to the cartilages of the lower three ribs and the aponeurosis of the linea alba.
Their lower and lateral attachments are to the inguinal ligament, the crest of the pelvis, and the fascia (connective tissue) of the lower back (erector spinae). At the lower end the internal oblique muscle fibers run almost horizontally. Both the external and internal oblique muscles are involved in flexing the rib cage and the pelvic bones together, sideward bending (lateral flexing) of the trunk, and rotating the trunk. The external obliques are referred to as “opposite side” rotators. Due to the muscle fiber arrangement, when you rotate to the left, the external oblique fibers on your right side facilitate the movement. Conversely, if you rotate to your right, the left external oblique fibers help with the movement. On the other hand, the internal oblique muscles are “same side” rotators. Thus, if you rotate to the left, the left internal oblique muscles facilitate the movement. When you rotate to the right, the right internal oblique muscles help cause the motion.
Due to the fact that the lower fibers of the internal oblique muscles run horizontally, they also are strong trunk rotators (Luttgens & Wells, 1992)#. Although most people think of the oblique muscles as being only frontal muscles, it is important to note that their fan-like fibers extend all the way around the sides to the lower back in much the same way a corset fits a person.
