Rectus Abdominis and Abdominal Obliques Anatomy Review

Anatomy of Abdominal Muscles: 

Rectus Abdominis and Abdominal Obliques

In this lesson, we will  reviewed the basic anatomy and actions of two abdominal muscles: the

rectus abdominis and the abdominal obliques.  

 

Under our abdominal skin we find fatty tissue.  This fatty tissue is separated from the muscles by the abdominal fascia.

Below is an image of the abdominal muscles from Gray’s Anatomy.  The rectus abdominis and the rectus sheath is colored gray in this this graphic.

Abdominal Muscles 

We will call the rectus abdominis, “rectus” for short in this lesson.

The abdominal obliques, which we will call “obliques,” are red colored and lateral to the rectus. In this image, the external obliques are labeled: “obliquis externus.”   The abdominal obliques attach to ribs, the inguinal ligament, the crest of the pelvis (ilium) and the abdominal aponeurosis and the thoracolumbar fascia.

The abdominal obliques are composed of three layers of fibers, running in different directions.  These layers are called:  the external obliques, the internal obliques, and the transverse abdominis.

The internal obliques are not labeled in this image. We cannot see the internal obliques, which are deep to the externals.  We also do not see the transverse abdominals, which are deep to the external and internal obliques.  We learn more about the unseen, deeper, flat abdominal muscles in another lesson.

 

 

 

 

 

 

 

 

The rectus and the obliques are labeled on the illustration below.

Rectus Abdominis and Abdominal Obliques.

The rectus, a large flat, compartmentalized muscle is often called the“six pack.”  Its upper six divisions become very apparent on body builders.  Actually, the rectus abdominis is divided into three, four, and five compartments on each side of the midline.  Some people do not have the same number of compartments on both sides.  For example, someone may have three compartments on one side and four on the other.  You can search the web for “uneven abdomen” images and you will find some wonderful variations on the six pack theme. 

Although most people’s abdomens look nothing like these very fit examples. In these images, we can distinguish the muscle shape better than we would be able to do in a in less developed abdomens.  In these images, we can easily see the thick connective tissue that creates the divisions of the muscle rectus muscles.

 

Below is another image of the rectus and the obliques in someone who works out often.  Again, notice the muscles are divided into compartments.   Large aponeuroses (flattened ligaments) form the rectus sheath and the linea alba.  The connective tissue running down the middle of the body is the linea alba.  The linea alba divides the rectus into right and left sides.

 

 

 

 

 

The large white tendon-like membrane covering the abdominal muscles in this image is called the abdominal aponeurosis.

 

 

 

 

 

 

 

 

The linea alba runs from the xiphoid process to the pubic symphysis.

 

The abdominal obliques attach to ribs, the inguinal ligament, the crest of the pelvis (ilium) and the abdominal aponeurosis and the thoracolumbar fascia.

 

 

Let’s move on to the actions of the abdominal muscles.


Actions of Abdominal Muscles

The abdominal muscles perform all sorts of important functions for us.  Some of the functions are protecting and keeping our internal organs in the body, controlling abdominal pressure, assisting in respiration, and stabilizing the spine while we do all sorts of activities.

Below is an image of the rectus and the obliques in action.

Abdominal Muscles in Action. The athlete is holding a weight behind his head to increase the work of the muscles.

The athlete below is doing a crunch that engages these muscles in trunk rotation.

Note the “six pack” rectus abdominis. The large dense connective tissue creates the muscular compartments. Notice where the obliques attach to the connective tissue of the rectus.

The rectus flexes the trunk, while the obliques flex and laterally bend the trunk.


In this lesson, we have reviewed the basic anatomy and actions of two abdominal muscles: the

rectus abdominis and the abdominal obliques.