Skin, Camper's and Scarpa's fascia, three muscle layers, transversalis fascia, extraperitoneal fat, peritoneum
Mnemonic
“Skin, Camper’s, Scarpa’s, three muscles, transversalis, peritoneum”:
- Skin
- Camper’s fascia - the fatty superficial layer
- Scarpa’s fascia - the membranous layer
- External oblique - fibres run downwards and forwards, “hands in pockets”
- Internal oblique - fibres run upwards and forwards, at right angles
- Transversus abdominis - fibres run transversely
- Transversalis fascia
- Extraperitoneal fat, then parietal peritoneum
“Camper is fatty, Scarpa is membranous”, and Scarpa’s continues into the perineum as Colles’ fascia, which is why extravasated urine from a ruptured urethra tracks into the scrotum and anterior abdominal wall but not into the thigh, where Scarpa’s fuses with the fascia lata.
The three muscle layers are the same three that form the spermatic cord coverings as the testis descends, giving external spermatic fascia, cremasteric fascia and internal spermatic fascia.
Expansion
From outside in:
- Skin
- Camper’s fascia - the fatty superficial layer
- Scarpa’s fascia - the membranous superficial layer
- External oblique
- Internal oblique
- Transversus abdominis
- Transversalis fascia
- Extraperitoneal fat
- Parietal peritoneum
The three flat muscles run in different directions, external oblique downwards and forwards (hands in pockets), internal oblique upwards and forwards, transversus horizontally. That criss-cross arrangement gives the wall its strength in the same way as plywood.
In the midline the layers fuse as the linea alba, which is why a midline laparotomy is relatively bloodless and crosses no nerves.