Page 73 - Clinical Anatomy

ECA2 7/18/06 6:42 PM Page 58

58 The abdomen and pelvis

The fasciae and muscles of the

abdominal wall

Fasciae of the abdominal wall
There is no deep fascia over the trunk, only the superficial fascia. (If there
were, we would presumably be unable to take a deep breath or enjoy a large
meal!) This, in the lower abdomen, forms a superficial fatty layer (of Camper)
and a deeper fibrous layer (of Scarpa). The fatty layer is continuous with the
superficial fat of the rest of the body, but the fibrous layer blends with the
deep fascia of the upper thigh, extends into the penis and scrotum (or labia
majora), and into the perineum as Colles’ fascia. In the perineum it is
attached behind to the perineal body and posterior margin of the perineal
membrane and, laterally, to the rami of the pubis and ischium. It is because
of these attachments that a rupture of the urethral bulb may be followed by
extravasation of blood and urine into the scrotum, perineum and penis and
then into the lower abdomen deep to the fibrous fascial plane, but not by
extravasation downwards into the lower limb, from which the fluid is
excluded by the attachment of the fascia to the deep fascia of the upper
thigh.

Nerve supply

The segmental nerve supply of the abdominal muscles and the overlying
skin is derived from T7 to L1. This distribution can be mapped out approxi-
mately if it is remembered that the umbilicus is supplied by T10 and the
groin and scrotum by L1 (via the ilio-inguinal and iliohypogastric nerves—
see Fig. 140).

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 3in (7.5cm) horizontal line from
the 5th, 6th and 7th costal cartilages and is inserted for a length of
1in (2.5cm) 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 inter-
sections 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).