The abdominal wall is subdivided into the anterior wall, the right and left lateral walls, and the posterior wall. These walls are musculoaponeurotic, meaning they are composed of muscles and fascial layers, except for the posterior wall which is also made up by the lumbar vertebral column. This musculoaponeurotic wall functions to enclose and protect the abdominal viscera, stabilize and contribute to movements of the trunk, and also increase the intra-abdominal pressure which is needed during urination, defecation, vomiting, and assisting in childbirth.
Now, the anterior and lateral abdominal walls are collectively known as the anterolateral abdominal wall, mainly because the boundary between the two is not distinct. So the anterolateral abdominal wall extends from the thoracic cage down to the pelvis. More specifically, it’s bounded superiorly by the cartilages of the seventh through tenth ribs as well as the xiphoid process, and inferiorly by the inguinal ligament and superior margins of the anterolateral aspects of the pelvic girdle
The anterolateral wall is composed of many different layers. There’s 12 of them in total. The most superficial layer is the skin, which covers a superficial fatty layer of subcutaneous tissue, or fat, known as Camper fascia, which is a major site of fat storage. Deep to the Camper fascia, there is a membranous layer of subcutaneous tissue known as Scarpa fascia, which is continuous inferiorly with the superficial perineal fascia, or Colles fascia. And deep to the superficial fascial layers, there are 3 muscle layers, each covered in a layer of a deep fascia - so 6 layers in total. So right after Scarpa fascia, there’s the superficial investing fascia, followed by the most superficial muscular layer: the external oblique muscle. Then comes the intermediate investing fascia and the internal oblique muscle. And finally, there are the deep investing fascia and the transversus abdominis muscle.
Deep to the transversus abdominis is the transversalis fascia. And finally, for our two deepest layers, there is a thin layer of extraperitoneal fat which is just above the parietal peritoneum, which is the deepest layer of the abdominal wall and lines the abdominal cavity.
