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Embryological Muscle Layers of the Trunk

Epaxial Muscles:

  • Erector spinae
  • Multifidus
  • Seminspinalis & Splenius
  • All intervertebral muscles on dorsal side of spine

Hypaxial Muscles (divides into the following 5 straps):

  1. Ventral Muscles:
  • Infrahyoids
  • Sternalis (only present in 25% of population)
  • Rectus Abdominis & Pyramidalis
  1. Subvertebral Muscles
  • Longus Colli & Longus Capitis
  • Psoas
  1. Lateral Muscles (subdivides into the following 3 layers):

a) External Layer:

  • Scalenus posterior
  • Levator scapulae
  • External intercostals
  • External abdominal obliques
  • Obturator externus
  • Superficial pelvic floor (Transversus perinei superf., Ischiocavernosus, Bulbospongiousus, Superficial external anal sphincter)

b) Intermediate Layer:

  • Scalenus medius
  • Internal intercostals
  • Internal abdominal obliques
  • Obturator internus
  • Middle layer of pelvic floor (Transverse perinei profundus, Sphincter urethrae, Deep internal anal sphincter)

c) Internal Layer:

  • Scalenus anterior
  • Transversus thoracis
  • Subcostals
  • Diaphragm
  • Levator Ani & Coccygeus

Summary of the article: Nielsen, Mark,’The Anatomist: Muscles of the Trunk’, Professional Bodyworkers Journal, Spring 198, p 42-48. All credit for good information goes to the original author, any mistakes are most likely mine. Robert Schleip, 2000