GENERAL CHARACTERISTICS
Limits. Surface limits of the abdomen are: superiorly - margins of costal arches and the xiphoid process; inferiorly - the iliac crests, inguinal folds (commonly corresponding to inguinal ligaments by projections) and the superior border of pubic bones sidewise from the symphysis. From the flanks, the regions of the abdomen are separated from the lumbar region by vertical lines drawn down from the anterior ends of the XI pair of ribs to iliac crests (this line is a continuation of the midaxillary line).
They mark the wall and cavity in the abdomen. The abdominal cavity, cavitas abdominis, includes the peritoneal cavity, cavitas peritonealis, viscera and the retroperitoneal space, spatium extraperitoneale.
The walls of the abdominal cavity do not correspond to the surface landmarks, because superiorly its superior wall - the diaphragm - enters the thoracic cavity as a cupola, while inferiorly the abdominal cavity is enlarged owing to the lesser pelvis. So, some abdominal organs are situated behind the ribs, in the intercostal spaces (the liver, spleen, and adrenal glands), while the loops of intestines descend into the lesser pelvic cavity.
The superior wall of the abdominal cavity is the diaphragm.
The inferior one is a conventional plane situated along the terminal line, linea termi-nalis, which separates the abdominal cavity from the peritoneal layer of the lesser pelvis.
The posterior wall is formed by lumbar vertebrae and muscles of the lumbar region.
The anterolateral wall is formed by the broad abdominal muscles (the external and internal oblique and the transversus)and rectus abdominis muscles.
All the walls except for the inferior are lined from inside by the parietal fascia, a part of the endoabdominal fascia, fascia endoabdominalis. The portions of the parietal fascia which adjoin to this or that wall are termed according to the muscle it adjoins f. diaphragmatica, f. psoatica, f. transversalis, etc.).