See also: peritoneum, belly button.
Anatomy of the (human) abdomen
In the mid-line a slight furrow extends
from the ensiform cartilage above to the symphysis pubis
below; this marks the linea alba in the abdominal wall, and
about its middle point is the umbilicus or navel. On each
side of it the broad recti muscles can be seen in muscular
people. The outline of these muscles is interrupted by
three or more transverse depressions indicating the lineae
transversae in the recti; there is usually one about the
ensiform cartilage, one at the umbilicus, and one between;
sometimes a fourth is present below the umbilicus. The upper
lateral limit of the abdomen is the subcostal margin formed
by the cartilages of the false ribs (8, 9, 10) joining one
another; the lower lateral limit is the anterior part of the
crest of the ilium and Poupart's ligament running from the
anterior superior spine of the ilium to the spine of the pubis; these lower limits are marked by definite
grooves. Just above the pubic spine is the external abdominal
ring, an opening in the muscular wall of the abdomen for
the spermatic cord to emerge in the male. The most modern
method of marking out the abdominal contents is to draw
three horizontal and two vertical lines; the highest of the
former is the transpyloric line of C. Addison, which is situated half-way between the suprasternal
notch and the top of the symphysis pubis; it often cuts the
pyloric opening of the stomach an inch to the right of the
mid-line. The hilum of each kidney is a little below it,
while its left end approximately touches the lower limit
of the spleen. It corresponds to the first lumbar vertebra
behind. The second line is the subcostal,
drawn from the lowest point of the subcostal arch (tenth
rib); it corresponds to the upper part of the third lumbar
vertebra, and is an inch or so above the umbilicus; it indicates
roughly the transverse colon, the lower ends of the kidneys,
and the upper limit of the transverse (3rd) part of the
duodenum. The third line is called the intertubercular, and runs across between the two rough
tubercles, which can be felt on the outer lip of the crest
of the ilium about two and a half inches from the anterior
superior spine. This line corresponds to the body of the
fifth lumbar vertebra, and passes through or just above
the ileo-caecal valve where the small intestine joins the large. The two vertical or mid-Poupart lines are drawn from
the point midway between the anterior superior spine and the
pubic symphysis on each side vertically upward to the costal
margin. The right one is the most valuable, as the ileo-caecal
valve is situated where it cuts the intertubercular line,
while the orifice of the vermiform appendix is an inch lower
down. At its upper part it meets the transpyloric line at
the lower margin of the ribs, usually the ninth, and here
the gallbladder is situated. The left mid-Poupart line
corresponds in its upper three-quarters to the inner edge of
the descending colon. The right subcostal margin corresponds
to the lower limit of the liver, while the right nipple is
about half an inch above the upper limit of this viscus.