The abdominal walls are lined by one continuous layer of connective tissue lying between the parietal peritoneum and the muscles. This fascial lining is continuous below with a similar layer of fascia lining the walls of pelvis.
Customarily, the fascia of this region is named according to the structure it lines. For instance;
- Diaphragmatic fascia covers the undersurface of diaphragm
- Transversalis fascia lines the transversus abdominis muscle
- Psoas fascia covers the psoas muscle
- Quadratus lumborum fascia covers the quadratus lumborum muscle
- Fascia iliaca covers the iliacus muscle
They all have different names but in fact they are regions of the same fascial lining without any discontinuity. The abdominal lymph and blood vessels lie within this fascia lining, whereas the principal nerves lie outside it. This is a very important point to remember and its significance can be understood by recalling the structure of femoral sheath.
The femoral sheath is a downward prolongation of abdominal fascial lining into the lower limbs. It covers the femoral vessels and lymphatics for about 1.5 inches into the thigh. But the femoral nerve, which is the principal nerve of lower limb, lies outside this sheath. The reason is that the major nerves lie outside the fascial envelope.
The fascial lining of the abdominal wall perform some important function in certain areas. For example, inferior to the level of anterior superior iliac spines, the posterior wall of rectus sheath doesn’t contain the muscular aponeuroses. In this region, it is formed by the fascia transversalis and peritoneum, both of which form part of fascial lining of the abdominal wall.