Anatomically, there are nine defined regions of interest. In clinical practice, however, these regions are defined imprecisely.
The abdomen can be divided into four quadrants, using a horizontal line and a vertical line that intersect at the umbilicus.
Layers of the Abdominal Wall
The anterolateral abdominal wall is made up of the following:
- Superficial fascia (fatty [Camper] and membranous [Scarpa])
- Deep fascia
- Aponeuroses of the muscle layers—anterior wall
- External oblique muscle—lateral wall
- Internal oblique muscle—lateral wall
- Transversus abdominis muscle—lateral wall
- Transversalis fascia
- Extraperitoneal fat
- Parietal peritoneum
The inguinal canal is an oblique passage through the inguinal region and a site of inguinal hernias (both direct and indirect). During embryonic development, the testes and spermatic cord (in males) and the round ligament (in females) descend through the inguinal canal.
Boundaries of the inguinal canal:
- Deep inguinal ring: Oval opening in the fascia transversalis lateral to the inferior epigastric vessels.
- Superficial inguinal ring: Triangular defect in the aponeurosis of the external oblique muscle, lateral to the pubic tubercle.
- Anterior wall: Aponeurosis of the external oblique muscle with some of the internal
oblique aponeurosis laterally.
- Posterior wall: Mainly transversalis fascia, with the conjoint tendon (falx inguinalis)
medially. The conjoint tendon is the merger of the internal abdominal oblique and
transverse abdominis aponeuroses.
- Roof: Internal oblique and transverse abdominal muscles.
- Floor: Inguinal and lacunar ligaments.
Anatomic region bounded by inferior epigastric artery, rectus abdominal muscle, and
inguinal ligament. Direct hernias pass through this triangle.
The femoral triangle is the anatomic region of the upper inner thigh bounded by the following:
- Superiorly: Inguinal ligament
- Laterally: Sartorius muscle
- Medially: Adductor longus muscle
Just below the inguinal ligament, there is a femoral sheath (fascial tube containing the
femoral vein, artery, and canal, the last of which contains lymphatics). The femoral nerve (L2–L4) lies outside of the sheath.