CHAPTER X.
THE ABDOMEN AND THE ORGANS OF DIGESTION AND EXCRETION.
The Abdominal Cavity.—Below the diaphragm and
separated from the lowest cavity of the trunk, the
pelvis, only by an invisible plane drawn through the
brim of the true pelvis, is the abdominal cavity, which
may be said in a general way to contain the organs
of digestion and the kidneys. It is protected behind
by the vertebræ and anteriorly by the lower ribs above
and below by muscular walls, which make possible the
complete bending of the body. These muscles are
for the most part large and very strong and the greater
number are inserted, in part at least, into a median
tendinous line, the linea alba, which passes from the
ensiform cartilage of the sternum above to the symphysis
pubis below.
Muscles.—The external obligue muscles form the outermost layer of the abdominal wall. They rise from the external surface of the eight lower ribs on either side and are inserted in the anterior half of the iliac crest as well as by aponeurosis in the linea alba, where each joins its fellow from the opposite side, the fibers running downward and inward like the fingers in the trouser's pocket. Along the lower border of the aponeurosis is a broad fold, Poupart's ligament. The internal oblique rises on either side from the outer half of Poupart's ligament and the anterior part of the crest of the ilium and is inserted into the crest of the os pubis, the cartilages of the lower ribs, and the linea alba. Its fibers run at right angles to those of the external oblique. These oblique muscles serve to compress the viscera, to flex the body, and also assist in expiration.
