Part of the anterior abdo wall
Fibres run anteromedially

Origins

Thoracolumbar fascia
Iliac crest
Lateral 2/3 inguinal ligament

Insertions

Lower 3 ribs (10-12) and costal cartilages
Xiphoid process
Linea alba
Pubic crest
Pectineal line

Thoracoabdominal nerve (T6-T11)
Subcostal nerve (T12)
iliohypogastric nerve (L1)
ilioinguinal nerve (L1)