Rectus abdominis muscle
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Rectus_abdominis_muscle".

Rectus abdominis
The human rectus abdominis muscle.
Latin	musculus rectus abdominis
Gray's	subject #118 415
Origin	pubis
Insertion	Costal cartilage of ribs 5-7, xiphoid process of sternum
Artery	inferior epigastric artery
Nerve	segmentally by thoraco-abdominal nerves (T7 to T12)
Action	flexion of trunk/lumbar vertebrae
Antagonist	Erector spinae
Dorlands /Elsevier	m_22/12550436

The rectus abdominis muscle (commonly known as "abs") is a paired muscle running vertically on each side of the anterior wall of the human abdomen (and in some other animals). There are two parallel muscles, separated by a midline band of connective tissue called the linea alba (white line). It extends from the pubic symphysis/pubic crest inferiorly to the xiphisternum/xiphoid process and lower costal cartilages (5-7) superiorly.

It is contained in the Rectus sheath.

The rectus is usually crossed by three fibrous bands called the tendinous inscriptions. Colloqiual names for the appearance of a well-defined rectus abdominis include a six pack and "washboard abs", and often carry cultural connotations of superior physical fitness. While the "sixpack" is by far the commonest configuration of the muscle bellies of the rectus, there exist rare anatomic variations which result in the appearance of eight (four per side) muscle segments ("eightpack"), ten, or (even rarer) asymmetrically arranged segments. All these variations are functionally equivalent.

Function

The rectus abdominis is a key postural muscle. It is responsible for flexing the lumbar spine, as when doing a 'crunch'. The rectus abdominis can play a role in respiration in the event the patient is short of breath.

Blood supply

A Mathes and Nahai Type III muscle (2 dominant pedicles)

1 - The inferior epigastric artery and vein (or veins) run superiorly on the posterior surface of the rectus abdominis, enter the rectus fascia at the arcuate line, and help to supply the muscle with blood.

2 - superior epigastric artery ( a terminal branch of the internal thoracic)

Also has small segmental contribution from lower 6 intercostal arteries

Location

A man with well-developed abdominal muscles (a "six-pack").

A teenager with low body fat, revealing slightly developed abdominal muscles

The Rectus abdominis is a long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba.

It is much broader, but thinner, above than below, and arises by two tendons;

• the lateral or larger is attached to the crest of the pubis,
• the medial interlaces with its fellow of the opposite side, and is connected with the ligaments covering the front of the symphysis pubis.

The muscle is inserted by three portions of unequal size into the cartilages of the fifth, sixth, and seventh ribs.

The upper portion, attached principally to the cartilage of the fifth rib, usually has some fibers of insertion into the anterior extremity of the rib itself.

Some fibers are occasionally connected with the costoxiphoid ligaments, and the side of the xiphoid process.

Animals

A feline rectus abdominis muscle, from a common housecat. This specimen has some remaining fascia and also shows the external obliques.

The Rectus Abdominis is similar in most vertebrates. The most obvious difference between animal and human abdominal musculature is that in animals, there are a different number of tendinous intersections.

Additional images

Anterior surface of sternum and costal cartilages.	The interfoveolar ligament, seen from in front.	Diagram of sheath of Rectus.	Diagram of a transverse section through the anterior abdomina wall, below the linea semicircularis.
The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side.	Horizontal disposition of the peritoneum in the lower part of the abdomen.	Transverse section through the middle of the first lumbar vertebra, showing the relations of the pancreas.	The left side of the thorax.
Surface anatomy of the front of the thorax and abdomen.	Muscles of the trunk

External links

• LUC reca
• 168165454 at GPnotebook
• SUNY Figs 04:04-07 - "Muscles of the anterior chest wall with the pectoralis major muscles removed."
• SUNY Labs 18:01-0115 - "Thoracic Wall: The Anterior Thoracic Wall"
• SUNY Figs 35:06-07 - "Incision and reflection of the external abdominal oblique muscle."
• SUNY Figs 35:07-01 - "Incision and reflection of the internal abdominal oblique muscle."
• SUNY Labs 35:10-0100 - "Anterior Abdominal Wall: The Rectus Abdominis Muscle"
• Cross section at UV pembody/body12a
• Rectus+abdominis+muscle at eMedicine Dictionary
• Roche Lexicon - illustrated navigator, at Elsevier 25466.180-1