Muscles of the Abdominal Wall

The walls of the chest and pelvic regions are supported directly by bone, but those of the abdomen are not. Instead, the anterior and lateral walls of the abdomen are composed of layers of broad, flattened muscles. These muscles connect the rib cage and vertebral column to the pelvic girdle. A band of tough connective tissue, called the linea alba, extends from the xiphoid process of the sternum to the symphysis pubis. It is an attachment for some of the abdominal wall muscles.

Contraction of these muscles decreases the volume of the abdominal cavity and increases the pressure inside. This action helps force air out of the lungs during forceful exhalation and also aids in defecation, urination, vomiting, and childbirth.

The abdominal wall muscles are shown in figure 9.33, reference plate 62, and are listed in table 9.10. They include the following:

External oblique Transversus abdominis

Internal oblique Rectus abdominis

The external oblique (eks-ter'nal o-blek) is a broad, thin sheet of muscle whose fibers slant downward from the lower ribs to the pelvic girdle and the linea alba. When this muscle contracts, it tenses the abdominal wall and compresses the contents of the abdominal cavity.

Internal oblique

Rectus abdominis External oblique Internal oblique

Transversus abdominis

External oblique i

Internal oblique

External oblique i

External Oblique And Internal Oblique

Rectus abdominis External oblique Internal oblique

Transversus abdominis

Transversus abdominis

Transversus abdominis

Peritoneum Transversus abdominis

Internal oblique

External oblique —J

Skin

(e) Rectus abdominis

Figure 9.33

(a-d) Isolated muscles of the abdominal wall. (e) Transverse section through the abdominal wall.

(e) Rectus abdominis

Figure 9.33

(a-d) Isolated muscles of the abdominal wall. (e) Transverse section through the abdominal wall.

Ü9II 1 Muscles of the

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