Muscle
Internal oblique
Abdominal layer with regionally changing fiber direction
High-yield
Unilateral contraction assists rotation toward the contracting side. Inferior fibers contribute to cremaster and may unite with transversus in the conjoint tendon.
Overview
Internal oblique sits between external oblique and transversus abdominis. Its upper and middle fibers generally rise toward the ribs and midline, while lower fibers take a different course toward the groin. Its aponeurosis contributes to the rectus sheath.
Reference facts
- Origin
- Thoracolumbar fascia, iliac crest and the lateral portion of the inguinal ligament.
- Insertion
- Fibers reach ribs 10–12 and the linea alba; inferior aponeurotic fibers attach near the pubis.
- Action
- Supports and compresses the abdominal contents; assists trunk flexion and same-side rotation.
- Innervation
- Lower thoracoabdominal nerves, subcostal nerve and L1 branches, including iliohypogastric and ilioinguinal nerves.
- Blood supply
- Lower intercostal and deep circumflex iliac arterial branches contribute to its supply.
Clinical correlation
Cremaster is derived partly from this muscle. Its reflex contraction depends on an intact sensory pathway and the genital branch of the genitofemoral nerve, linking the groin to L1–L2 spinal segments.
Frequently asked questions
What does the internal oblique do?
Supports and compresses the abdominal contents; assists trunk flexion and same-side rotation.
What nerve innervates the internal oblique?
The internal oblique is innervated by the lower thoracoabdominal nerves, subcostal nerve and L1 branches, including iliohypogastric and ilioinguinal nerves.
Where does the internal oblique attach?
Origin: Thoracolumbar fascia, iliac crest and the lateral portion of the inguinal ligament. Insertion: Fibers reach ribs 10–12 and the linea alba; inferior aponeurotic fibers attach near the pubis.
What is the blood supply of the internal oblique?
The internal oblique is supplied by the lower intercostal and deep circumflex iliac arterial branches contribute to its supply.