Logan Steele
The abdominal muscles form the abdominal walls, connecting the thorax and pelvis. There are five paired muscles and their respective aponeuroses, divided into two main groups: the lateral flat muscle group, situated on either side of the abdomen, and the vertical muscles, located near the mid-line of the body. The lateral flat muscle group includes three muscles: external oblique, internal oblique, and transversus abdominis. The vertical muscles include the rectus abdominis and pyramidalis.
| Characteristics | Values |
|---|---|
| Number of muscles | Five paired muscles |
| Muscle groups | Lateral flat muscle group and vertical muscle group |
| Lateral flat muscle group | External oblique, internal oblique and transversus abdominis |
| Vertical muscle group | Rectus abdominis and pyramidalis |
| Flat muscles | Three, situated laterally on either side of the abdomen |
| Vertical muscles | Two, situated near the mid-line of the body |
| Flat muscle fibres | Run in differing directions and cross each other |
| Flat muscle function | Strengthen the wall and decrease the risk of abdominal contents herniating through the wall |
| Flat muscle aponeurosis | Covers the vertical rectus abdominis muscle |
| Flat muscle aponeuroses | Become entwined in the midline to form the linea alba |
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What You'll Learn
Anterolateral abdominal wall muscles
The abdominal muscles are divided into two groups: the anterolateral abdominal wall muscles and the posterior abdominal wall muscles. The anterolateral abdominal wall muscles are made up of two vertical muscles located on the midline (bisected by linea alba): the rectus abdominis and the pyramidalis. There are also three flat muscles on the anterolateral side arranged from superficial to deep: the external abdominal oblique, the internal abdominal oblique, and the transversus abdominis.
The three flat muscles are situated laterally on either side of the abdomen. Their fibres run in differing directions and cross each other, strengthening the wall and decreasing the risk of abdominal contents herniating through the wall. In the anteromedial aspect of the abdominal wall, each flat muscle forms an aponeurosis (a broad, flat tendon), which covers the vertical rectus abdominis muscle. The aponeuroses of all the flat muscles become entwined in the midline, forming the linea alba (a fibrous structure that extends from the xiphoid process of the sternus to the pubic symphysis).
The most superficial, largest, and thickest of the three anterolateral abdominal wall muscles originates from the lower seven ribs and runs obliquely from superior/lateral to inferior/medial (hands in pocket orientation) to insert on the anterior one-half of the iliac crest. The most inferior extension folds posteriorly and superiorly to form the inguinal ligament. At the mid-clavicular line, the muscle belly ends, but the aponeurosis extends medially to the linea alba, contributing to the anterior rectus sheath.
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Posterior abdominal wall muscles
The posterior abdominal wall is a complex area of the body made up of muscles, vessels and nerves that work together to hold abdominal organs in place, adjust our posture, stabilise the hip joint and even flex our thighs. The main paired muscles of the posterior abdominal wall include psoas major, iliacus and quadratus lumborum. The psoas major is a long, thick muscle that lies lateral to the lumbar vertebrae. The muscles of the posterior abdominal wall attach to the lumbar vertebral bodies, the transverse process and the 12th rib. The lumbar vertebrae have a forward convexity and paravertebral gutters lie deep to each side of this convexity.
The posterior abdominal wall primarily serves as protection for the retroperitoneal organs. It is mostly muscular and contributed to by the diaphragm, paraspinal, quadratus lumborum, iliacus, and psoas muscles. The psoas and quadratus lumborum muscles are sometimes included as the posterior compartment of the retroperitoneum.
The abdominal wall performs several vital functions. It contains and provides a scaffold for the development and functioning of abdominal viscera. All layers contribute to a degree of physical protection of the organs. The abdominal muscles may be divided broadly into anterolateral and posterior components. Posterior muscles include psoas major and quadratus lumborum bilaterally. The abdominal muscles contribute to movements of the trunk, including flexion, extension, lateral flexion, and rotation.
There are two fasciae in the posterior abdominal wall: the psoas fascia and thoracolumbar fascia. The thoracolumbar fascia splits into the posterior, middle, and anterior layers. The muscles of the posterior wall are sandwiched between these layers, and the nerves generally course from superomedial to inferolateral in the retroperitoneum.
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Lateral flat muscle group
The abdominal muscles are divided into two broad groups: the anterolateral and posterior walls. The lateral flat muscle group is situated on either side of the abdomen and includes three muscles: the external oblique, internal oblique and transversus abdominis. These muscles are stacked upon one another, with their fibres running in differing directions and crossing each other to strengthen the wall and decrease the risk of abdominal contents herniating through the wall.
The external oblique is the most superficial, largest, and thickest of the three muscles. It originates from the lower seven ribs and runs obliquely from superior/lateral to inferior/medial (hands in pocket orientation) to insert on the anterior one-half of the iliac crest. The most inferior extension folds posteriorly and superiorly to form the inguinal ligament. At the mid-clavicular line, the muscle belly ends, but the aponeurosis extends medially to the linea alba, contributing to the anterior rectus sheath.
The internal oblique is the middle layer of the three muscles, originating from the iliopsoas fascia, lateral iliac crest, and lumbodorsal fascia. The transversus abdominis is the deepest of the three muscles.
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Vertical muscles
The abdominal muscles are the muscles that form the abdominal walls, connecting the thorax and pelvis. The abdominal wall consists of five paired muscles and their respective aponeuroses. The muscles of the anterolateral abdominal wall are divided into two main groups: the lateral flat muscle group and the vertical muscle group.
The vertical muscles are two muscles situated near the midline of the body. They are stacked upon the three flat muscles located laterally in the abdominal wall. Their fibres run in differing directions and cross each other, strengthening the wall and decreasing the risk of abdominal contents herniating through the wall. The vertical muscles are:
- Rectus abdominis
- Pyramidalis
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Aponeuroses
The abdominal muscles are divided into two groups: anterolateral and posterior walls. The anterolateral abdominal wall muscles consist of two vertical muscles located on the midline (bisected by linea alba): rectus abdominis and pyramidalis. There are also three flat muscles on the anterolateral side arranged from superficial to deep: external abdominal oblique, internal abdominal oblique, and transversus abdominis.
The flat muscles are situated laterally on either side of the abdomen. The vertical muscles are located near the mid-line of the body. The flat muscles are stacked upon one another, with their fibres running in differing directions and crossing each other. This strengthens the wall and decreases the risk of abdominal contents herniating through the wall.
In the anteromedial aspect of the abdominal wall, each flat muscle forms an aponeurosis (a broad, flat tendon), which covers the vertical rectus abdominis muscle. The aponeuroses of all the flat muscles become entwined in the midline, forming the linea alba (a fibrous structure that extends from the xiphoid process of the sternus to the pubic symphysis). The linea alba is a thick band of connective tissue that runs down the midline of the abdomen, from the xiphoid process of the sternum to the pubic symphysis. It is formed by the fusion of the aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles.
The aponeurosis of the external oblique muscle is the most superficial and largest of the aponeuroses. It originates from the lower seven ribs and runs obliquely from superior/lateral to inferior/medial (hands in pocket orientation) to insert on the anterior one-half of the iliac crest. The most inferior extension folds posteriorly and superiorly to form the inguinal ligament. At the mid-clavicular line, the muscle belly ends, but the aponeurosis extends medially to the linea alba, contributing to the anterior rectus sheath.
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Frequently asked questions
The abdominal muscles are the muscles forming the abdominal walls, the abdomen being the portion of the trunk connecting the thorax and pelvis.
The muscles of the anterolateral abdominal wall are divided into two main groups: the lateral flat muscle group and the vertical muscles.
There are three muscles in the lateral flat muscle group: external oblique, internal oblique and transversus abdominis.
The vertical muscles are two muscles situated near the mid-line of the body.
The three flat muscles are situated laterally on either side of the abdomen. Their fibres run in differing directions and cross each other, strengthening the wall and decreasing the risk of abdominal contents herniating through the wall.
