Abdominal muscles T7 - T12, L1

External oblique:Most superficial.
From: lower 8 ribs, downward and ventrally
To: iliac crests and linea alba.

Internal Oblique: Middle layer.
From: inguinal ligament and iliac crest, upward and dorsally
To: anterolateral cartilage of last 3 ribs and linea alba.

Transverse abdominous:Deepest.
From: last 6 ribs, lumbar fascia, iliac crest and inguinal ligament, circumferentialy
To: rectus sheath.

Rectus abdominous:
From: pubis
To: costal cart of ribs 5,6,7.

Function of the abdominal muscles: To increase abdominal pressure. This is usually for expiration, yet it can aide inspiration by storing expiratory force which when released can initiate inspiration, and may help position the diaphragm.