Linea alba (white line)A band of fibrous tissue from the xiphoid process to the pubic symphysis, formed where the flat tendons of the two sides meet between the rectus abdominis muscles.
Rectus sheath, anterior layerAbove the arcuate line it is the external oblique aponeurosis plus the front half of the split internal oblique aponeurosis. The tendinous intersections hold fast to its deep side.
External oblique (external abdominal oblique)The largest and most superficial of the three flat muscles. It arises by eight slips from ribs 5 to 12, bends the trunk to its own side and turns it to the opposite side.
Rectus abdominis (abs)Runs from the pubic crest and symphysis up to the xiphoid process and the cartilages of ribs 5 to 7. It flexes the vertebral column, as in a sit-up, and lies inside the rectus sheath.
Tendinous intersections (six-pack lines)Three bands of collagen fibers that cut each rectus abdominis into segments, the look known as a six-pack. One lies at the navel, one at the tip of the xiphoid process and one midway between.
Transversus abdominis (corset muscle)The innermost of the three flat muscles. Its fibers run across the abdomen to the linea alba, and it compresses the abdominal contents, as in forceful exhaling.
Internal oblique (internal abdominal oblique)The middle flat muscle. It arises from the thoracolumbar fascia, the iliac crest and the inguinal ligament, reaches ribs 10 to 12 and the linea alba, and turns the trunk to its own side.
Quadratus lumborum (QL)Runs from the iliac crest and the iliolumbar ligament to the last rib and vertebrae L1 to L4. One side working alone bends the spine to that side, and the muscle steadies rib 12.
Muscles only 4
PyramidalisA small triangular muscle inside the rectus sheath, in front of the rectus abdominis. It runs from the pubic symphysis and pubic crest to the linea alba, and some people have none.
Psoas majorArises from vertebrae T12 to L5 and joins the iliacus to form the iliopsoas. The two insert on the lesser trochanter and flex the thigh at the hip. The name comes from the Greek for muscles of the loins.
Psoas minorA slender muscle in front of the psoas major, from vertebrae T12 and L1 to the rim of the pelvis. It is often absent: many people have none.
IliacusA flat, triangular muscle that fills the iliac fossa. It joins the psoas major to form the iliopsoas, which flexes the thigh at the hip.
Superficial layer 5
Linea semilunaris (semilunar line)A curved line along the outer border of the rectus abdominis, from the ninth rib cartilage to the pubic tubercle. Here the internal oblique aponeurosis splits to pass around the rectus. Also called the Spigelian line.
Umbilicus (navel)The scar where the umbilical cord was attached. It lies on the linea alba, usually level with the junction of vertebrae L3 and L4, and the skin at its level is supplied by spinal nerve T10.
Aponeurosis of the external obliqueThe flat tendon of the external oblique. The muscle turns to tendon near the midclavicular line, the sheet joins the front of the rectus sheath, and below it forms the inguinal ligament.
Inguinal ligament (groin ligament)A band formed by the external oblique aponeurosis, from the anterior superior iliac spine to the pubic tubercle. The psoas major, the iliacus and the femoral vessels pass under it into the thigh.
Superficial inguinal ringThe exit of the inguinal canal: a triangular opening in the external oblique aponeurosis just above the pubic crest, about 1 cm above and to the side of the pubic tubercle.
Deeper layers 3
Rectus sheath, posterior layerThe back half of the split internal oblique aponeurosis plus the transversus abdominis aponeurosis. It lies behind the rectus abdominis and stops at the arcuate line.
Arcuate line (semicircular line)The free lower edge of the posterior layer of the rectus sheath, about midway between umbilicus and pubic symphysis. Below it all three aponeuroses pass in front of the rectus abdominis.
Transversalis fasciaThe fascia that lines the inner surface of the transversus abdominis. Below the arcuate line it is all that separates the rectus abdominis from the peritoneum.
Back wall 2
Central tendon of the diaphragmThe flat tendon at the top of the dome, in three leaflets. The muscle fibers of the diaphragm insert into it and not into bone, and the inferior vena cava passes through it.
Right crus of the diaphragmA tapering band that anchors the diaphragm to vertebrae L1 to L3. The left crus is shorter and reaches only L2. A sling of fibers from the right crus surrounds the opening for the esophagus.
How this list was compiled: Part names and detail lines were checked on 2026-09-20, for facts only and written in our own words, against OpenStax Anatomy and Physiology 2e, sections 11.4 Axial Muscles of the Abdominal Wall, and Thorax and 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs (https://openstax.org/books/anatomy-and-physiology-2e/pages/11-4-axial-muscles-of-the-abdominal-wall-and-thorax, https://openstax.org/books/anatomy-and-physiology-2e/pages/11-6-appendicular-muscles-of-the-pelvic-girdle-and-lower-limbs). OpenStax does not name the pyramidalis, the inguinal ligament, the arcuate line, the linea semilunaris or the transversalis fascia, so these and the finer attachments were checked on Wikipedia: https://en.wikipedia.org/wiki/Abdominal_external_oblique_muscle, https://en.wikipedia.org/wiki/Abdominal_internal_oblique_muscle, https://en.wikipedia.org/wiki/Transverse_abdominal_muscle, https://en.wikipedia.org/wiki/Rectus_abdominis_muscle, https://en.wikipedia.org/wiki/Rectus_sheath, https://en.wikipedia.org/wiki/Arcuate_line_of_rectus_sheath, https://en.wikipedia.org/wiki/Linea_alba_(abdomen, https://en.wikipedia.org/wiki/Linea_semilunaris, https://en.wikipedia.org/wiki/Tendinous_intersection, https://en.wikipedia.org/wiki/Inguinal_ligament, https://en.wikipedia.org/wiki/Superficial_inguinal_ring, https://en.wikipedia.org/wiki/Pyramidalis_muscle, https://en.wikipedia.org/wiki/Transversalis_fascia, https://en.wikipedia.org/wiki/Navel, https://en.wikipedia.org/wiki/Quadratus_lumborum_muscle, https://en.wikipedia.org/wiki/Psoas_major_muscle, https://en.wikipedia.org/wiki/Psoas_minor_muscle, https://en.wikipedia.org/wiki/Iliacus_muscle, https://en.wikipedia.org/wiki/Thoracic_diaphragm and https://en.wikipedia.org/wiki/Central_tendon_of_diaphragm. Every name was checked again on 2026-09-30 against OpenStax sections 11.4 and 11.6, the same Wikipedia articles, and an independent second source for the names OpenStax does not give: TeachMeAnatomy, The Anterolateral Abdominal Wall (https://teachmeanatomy.info/abdomen/muscles/abdominal-wall/), The Posterior Abdominal Wall (https://teachmeanatomy.info/abdomen/muscles/posterior-wall/) and The Diaphragm (https://teachmeanatomy.info/thorax/muscles/diaphragm/), and Kenhub, Abdominal wall (https://www.kenhub.com/en/library/anatomy/posterior-abdominal-wall). Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced and no plate copied. Muscle carries fine lines that show the fiber direction; tendon and fascia are plain. Licence: own work
How it works
This abdominal muscles quiz peels the front of the trunk back layer by layer: external oblique, internal oblique, transversus abdominis, and the rectus abdominis inside its sheath. A second figure shows the back wall. There are 22 numbered parts to find or name.
Read the full guide
Upper figure: three flat layers and the rectus sheath
On the figure's right, which is your left, the outer layer is whole: the external oblique (3), its aponeurosis (6) and the front of the rectus sheath (2). On the other side it is removed. A window in the internal oblique (13) shows the transversus abdominis (12), and the rectus abdominis (10) is cut below the navel to show the posterior layer (14), the arcuate line (15) and the transversalis fascia (16).
Lower figure: the back wall
Parts 17 to 22 are on the back wall, seen from the front with the organs removed: the central tendon and right crus of the diaphragm, quadratus lumborum, psoas major, psoas minor and iliacus. The psoas minor is drawn on one side only, because many people have none.
Read the fiber direction: external oblique fibers slant like fingers in a front pocket, internal oblique fibers cross them, transversus fibers run straight across.
Under Start from, pick Simple: 8 core parts first, then Muscles only.
Left and right belong to the figure, not to you. The right crus of the diaphragm is on your left.
Questions and answers
Is there a muscles of the abdomen quiz without the sheaths and lines?
Yes. Under Start from, choose Muscles only. It asks 9 muscles and nothing else: external oblique, internal oblique, transversus abdominis, rectus abdominis, pyramidalis, quadratus lumborum, psoas major, psoas minor and iliacus.
What are the muscle layers of the abdominal wall, from outside in?
On the flank: external oblique, internal oblique, transversus abdominis, then the transversalis fascia. Near the midline the flat tendons of all three wrap the rectus abdominis as the rectus sheath and meet at the linea alba.
What is the rectus sheath made of?
Above the arcuate line, the front layer (2) is the external oblique aponeurosis plus the front half of the split internal oblique aponeurosis. The back layer (14) is the other half plus the transversus abdominis aponeurosis.
What changes at the arcuate line?
Above it, the rectus sheath has a layer behind the rectus abdominis. Below it, all three aponeuroses pass in front, so only the transversalis fascia lies behind the muscle. The line is about midway between navel and pubic symphysis.