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transversus abdominis (anatomy)
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Transversus abdominis is the deepest of the three anterolateral abdominal wall muscles. It arises from a number of sites:

  • internal surface of 7th to 12th costal cartilages with fibres interdigitating with those of the diaphragm
  • thoracolumbar fascia lateral to quadratus lumborum
  • anterior two-thirds of the iliac crest
  • lateral half of inguinal ligament

The fibres of transversus abdominis pass transversely around the abdominal wall deep to the internal oblique muscle. Anteriorly, they become aponeurotic.

The aponeurosis has two main insertions:

  • the rectus sheath:
    • fuses with aponeurosis of internal oblique to insert into linea alba
    • above the arcuate line, passes deep to rectus abdominis, whereas below this line it passes superficially
  • the pubic crest and pectineal line via the conjoint tendon

Transversus abdominis is innervated by the anterior primary rami of T7 to T12. The conjoint tendon is supplied by the ilioinguinal nerve (L1).

The actions of transversus abdominis are multiple:

  • support for the abdominal wall
  • role in maintenance of posture
  • trunk movements: flexion, extension, lateral flexion
  • raise intra-abdominal pressure e.g. for forced expiration, defaecation, micturition and parturition
  • via the conjoint tendon, to support the posterior wall of the inguinal canal