The muscles of the anterior abdominal wall

These are of considerable practical importance because their anatomy forms the basis of abdominal incisions.

The rectus abdominis (Fig. 43) arises on a 3 in (7.5 cm) horizontal line from the 5th, 6th and 7th costal cartilages and is inserted for a length of 1in (2.5 cm) into the crest of the pubis. At the tip of the xiphoid, at the umbilicus and half-way between, are three constant transverse tendinous intersections; below the umbilicus there is sometimes a fourth. These intersections are seen only on the anterior aspect of the muscle and here they adhere to the anterior rectus sheath. Posteriorly they are not in evidence and, in consequence, the rectus muscle is completely free behind. At each intersection, vessels from the superior epigastric artery and vein pierce the rectus.

The sheath in which the rectus lies is formed, to a large extent, by the aponeurotic expansions of the lateral abdominal muscles (Fig. 44).

Anterior layer of rectus sheath

Anterior layer of rectus sheath

Rectus Sheath Muscle Skeleton

Anterior layer of rectus sheath

Rectus abdominis

Tendinous intersection

External oblique

Ilio-inguinal nerve

Spermatic cord

Fig. 43 Anterior abdominal wall. The anterior rectus sheath on the left side has been reflected laterally.

Anterior layer of rectus sheath

Rectus abdominis

Tendinous intersection

External oblique

Ilio-inguinal nerve

Spermatic cord

Fig. 43 Anterior abdominal wall. The anterior rectus sheath on the left side has been reflected laterally.

Rectus Sheath
Fig. 44 The composition of the rectus sheath shown in transverse section (a) above the costal margin, (b) above the arcuate line and (c) below the arcuate line.

(a) Above the costal margin, the anterior sheath comprises the external oblique aponeurosis only; posteriorly lie the costal cartilages.

(b) From the costal margin to a point half-way between umbilicus and pubis, the external oblique and the anterior part of the internal oblique aponeurosis form the anterior sheath. Posteriorly lie the posterior part of this split internal oblique aponeurosis and the aponeurosis of transversus abdominis.

(c) Below a point half-way between umbilicus and pubis, all the aponeuroses pass in front of the rectus so that the anterior sheath here comprises the tendinous expansions of all three oblique muscles blended together. The posterior wall at this level is made up of the only other structures available—the transversalis fascia, (the thickened extraperitoneal fascia of the lower abdominal wall), and peritoneum.

The posterior junction between (b) and (c) is marked by the arcuate line of Douglas, which is the lower border of the posterior aponeurotic part of the rectus sheath. At this point the inferior epigastric artery and vein (from the external iliac vessels) enter the sheath, pass upwards and anastomose with the superior epigastric vessels which are terminal branches of the internal thoracic artery and vein. The rectus sheaths fuse in the midline to form the linea alba stretching from the xiphoid to the pubic symphysis.

The lateral muscles of the abdominal wall comprise the external and internal oblique and the transverse muscles. These correspond to the three layers of muscle of the chest wall—external, internal and innermost inter-costals, and, like them, have their neurovascular bundles running between the second and third layer. They are clinically important in making up the rectus sheath and the inguinal canal, and also because they must be divided in making lateral abdominal incisions.

Their attachments can be remembered when one bears in mind that they fill the space between the costal margin above, the iliac crest below, and the lumbar muscles covered by lumbar fascia behind. Medially, as already noted, they constitute the rectus sheath and thence blend into the linea alba from xiphoid to pubic crest.

The obliquus externus abdominis (external oblique) arises from the outer surfaces of the lower eight ribs and fans out into the xiphoid, linea alba, the pubic crest, pubic tubercle and the anterior half of the iliac crest.

From the pubic tubercle to the anterior superior iliac spine its lower border forms the aponeurotic inguinal ligament of Poupart.

The obliquus internus abdominis (internal oblique) arises from the lumbar fascia, the anterior two-thirds of the iliac crest and the lateral two-thirds of the inguinal ligament. It is inserted into the lowest six costal cartilages, linea alba and the pubic crest.

The transversus abdominis arises from the lowest six costal cartilages (interdigitating with the diaphragm), the lumbar fascia, the anterior two-thirds of the iliac crest and the lateral one-third of the inguinal ligament; it is inserted into the linea alba and the pubic crest.

Note that the external oblique passes downwards and forwards, the internal oblique upwards and forwards and the transversus transversely.

Note also that the external oblique has its posterior border free but the deeper two muscles both arise posteriorly from the lumbar fascia.

The Gymless Ab Toner

The Gymless Ab Toner

This is a video all about getting the best abs and learning how to get them the faster way possible.

Get My Free Video


Post a comment