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Internal and External Obliques Anatomy: Origin, Insertion, Action and Innervation

(Last Updated On: August 10, 2018)
Internal Oblique Muscle

Muscle Anatomy of the Internal Oblique

Origin: Lumbar fascia, anterior two-thirds of the iliac crest, and the lateral two-thirds of the inguinal ligament
Insertion: Costal margin, aponeurosis of the rectus sheath, conjoined tendon to the pubic crest and pectineal line, 10-12 rib
Actions: Unilaterally assists in lateral flexion and rotation of the spine. Bilaterally flexes the spine.
Innervation: Ventral primary rami of T7 to T12; conjoined tendon supplied by L1.
Blood Supply: Superior and inferior epigastric and deep circumflex iliac arteries.

Muscle Anatomy: Internal Oblique Actions

Primary Actions of the Internal Oblique

1.  Lateral flexion of the thoracic spine when acting unilaterally

  Agonists: Muscles located on the same side of movement

  1. Iliocostalis cervicis
  2. Iliocostalis thoracis
  3. Iliocostalis lumborum
  4. Longissimus cervicis
  5. Longissimus thoracis
  6. External oblique

  Antagonists: Same muscles on contralateral side

  1. Iliocostalis cervicis
  2. Iliocostalis thoracis
  3. Iliocostalis lumborum
  4. Longissimus cervicis
  5. Longissimus thoracis
  6. External oblique

Note: Semispinalis cervicis, semispinalis thoracis, and the intertransversarii assist with lateral flexion of the thoracic spine.

2. Lateral flexion of the lumbar spine when acting unilaterally

Agonists: Muscles located on the same side of movement

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Psoas major
  • External oblique

Antagonists: Same muscles on contralateral side

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Psoas major
  • External oblique

Note: The intertransversarii assist with lateral flexion of the lumbar spine.

3. Ipsilateral rotation of the trunk when acting unilaterally

Agonists: None

Secondary Actions of the Internal Oblique:

1. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists:

  • Rectus abdominis

  Antagonists:

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Spinalis thoracis
  • Semispinalis cervicis
  • Semispinalis thoracis

Note: External oblique and psoas major assist with flexion of the thoracic spine.

2. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists:

  • Rectus abdominis

  Antagonists:

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Spinalis thoracis

Note: External oblique and psoas major assist with flexion of the lumbar spine.

3. Assists with forced expiration

Agonists:

  • Serratus posterior inferior
  • Transversus abdominis

  Antagonists: 

  • Serratus posterior superior
  • Levatores costarum breves
  • Levatores costarum longi

Note: Rectus abdominis and external oblique assist with forced expiration.

External Oblique Muscle Origin, Insertion, Action, Innervation

Muscle Anatomy of the External Oblique

Origin: Angle of the 9th rib, blending with serratus anterior and from the angles of the 10th, 11th, and 12th ribs, blending with latissimus dorsi.
Insertion: Outer anterior half of the iliac crest, the inguinal ligament, the pubic tubercle and crest, and the aponeurosis of the anterior rectus sheath.
Actions: Unilaterally assists in lateral flexion and rotation of the spine. Bilaterally flexes the spine.
Innervation: Ventral primary rami of T7 to T12.
Blood Supply: Superior and inferior epigastric arteries

Muscle Anatomy: External Oblique Actions

Primary Actions of the External Oblique

1.  Lateral flexion of the thoracic spine when acting unilaterally

  Agonists:

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Internal oblique

  Antagonists: Same muscles on contralateral side

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Internal oblique

Note: Semispinalis cervicis, semispinalis thoracis, and the intertransversarii assist with lateral flexion of the thoracic spine.

2. Contralateral rotation of the trunk when acting unilaterally

Agonists:

  • Semispinalis cervicis
  • Semispinalis thoracis
  • Multifidus

Antagonists: Same muscles on contralateral side

  • Semispinalis cervicis
  • Semispinalis thoracis
  • Multifidus

Note: The rotatores assist with contralateral rotation of the trunk

3. Lateral flexion of the lumbar spine when acting unilaterally

Agonists: 

  • Iliocostalis lumborum,
  • Longissimus thoracis
  • Psoas major
  • Quadratus lumborum
  • Internal oblique

Antagonists: Same muscles on contralateral side

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Psoas major
  • Quadratus lumborum
  • Internal oblique

Note: The intertransversarii assist with lateral flexion of the lumbar spine.

Secondary Actions of the External Oblique:

1. Assists with flexion of the thoracic spine when acting bilaterally

  Agonists:

  • Rectus abdominis

  Antagonists:

  • Iliocostalis cervicis
  • Iliocostalis thoracis
  • Iliocostalis lumborum
  • Longissimus cervicis
  • Longissimus thoracis
  • Spinalis thoracis
  • Semispinalis cervicis
  • Semispinalis thoracis

Note: Internal oblique and psoas major assist with flexion of the thoracic spine.

2. Assists with flexion of the lumbar spine when acting bilaterally.

Agonists:

  • Rectus abdominis

Antagonists:

  • Iliocostalis lumborum
  • Longissimus thoracis
  • Spinalis thoracis

Note: Internal oblique and psoas major also assist with flexion of the lumbar spine.

3. Supports the abdominal wall

Agonists:

  • Rectus abdominis
  • Transversus abdominis
  • Internal oblique

Antagonists: None

4. Assists with forced expiration

Agonists:

  • Serratus posterior inferior
  • Transversus abdominis

  Antagonists: 

  • Serratus posterior superior
  • Levatores costarum breves
  • Levatores costarum longi

Note: Rectus abdominis and internal oblique assist with forced expiration.

For pain and symptom information see:

External Internal Oblique Muscles: Abdomen, Groin, Testicular Pain

Recommended Anatomy Books:

Anatomy Coloring Book

The Anatomy Coloring Book is one of the best study and reference books for beginning anatomy students. The diagrams are clearly labeled and allow you to see the relationship and placement of the various structures of the body. You will also be surprised how the act of coloring will help with recall. But this is not just a beginners book, it is also great for practitioners and therapists to have on hand to use with clients and patients to use as a visual reference.

Human Muscle Anatomy

The Trail Guide To The Body is another excellent book to help you learn the musculature of the human body. Though the book is geared toward massage therapists and physical therapist assistants, the book with its illustrations and text helps anyone gain a thorough understanding of the human musculoskeletal system and movement. I highly recommend this book for anyone studying anatomy and believe that MTs, PTAs, and teachers of body movements should have this book in their possession. I also highly recommend this book for the lay person who wants to gain understanding of the muscle, skeletal system and how our bodies move. This book will not disappoint!

Basic Clinical Massage Therapy

Out of the scores of books in my office Basic Clinical Massage Therapy is by far the most referenced book in my library. The musculoskeletal system is overlaid on human models allowing you to learn the precise location, origin and insertions of each muscle. The models are pictured in various poses throughout the book which also helps you visualize muscles in motion and their actions relationship with the skeletal structure and other muscles. Though it is written for massage therapists, it is an excellent book for anyone who wants to learn about the muscular system. MT's will benefit from recommended treatments for each muscle.

Muscle Anatomy Flashcards

Musculoskeletal Anatomy Flashcards Are you a student or professional therapist who needs to brush up on the musculoskeletal system? Dr. Joseph E. Muscolino DC has developed a comprehensive set of flashcards that will help develop a mind's picture of exactly where the muscles lie under the skin. A highly recommended study aid for students. Great for non students who want an easy comprehensive anatomy guide.

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