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

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