THE ABDOMINAL CAVITY. 381 



order to determine the various regions into which it is possible to divide it : 

 a matter of some importance, as it singularly facilitates the topographical 

 study of the contained viscera ; for to say that an organ is situated in 

 the abdomen, is a very vague reference to its precise situation, in conse- 

 quence of the great extent of this cavity. It is necessary, therefore, to 

 divide the abdomen into a certain number of peripheral regions which corre- 

 spond to the different parts of its wall, with a view to define the situation 

 of the organs lodged therein, yet without complicating anatomical de- 

 scription. Six principal regions are* recognised in the abdominal cavity. 



A. The superior, or sublumbar region, corresponds to the superior wall of 

 the abdomen : that is, to the psoas muscles and the bodies of the lumbar 

 vertebrae. It extends from the opening between the two pillars of the 

 diaphragm to the entrance to the pelvis. 



B. The inferior region, limited, laterally, by the hypochondriacs and 

 the flanks, commences, in front, at the xiphoid cartilage, and is prolonged 

 to the pubis ; it comprises all that portion of the abdomen which corre- 

 sponds to the linea alba and the two recti muscles. Its great extent 

 necessitates its subdivision into five secondary regions : The suprasternal 

 region, named the epigastric in Man, placed above the xiphoid cartilage of the 

 sternum ; the umbilical region, situated behind the preceding, and so named 

 in consequence of its including that part of the wall which is pierced by the 

 umbilicus ; the prepubic region the hypogastric or pubic of Man occupies 

 the space in front of the anterior border of the pubis; the two inguinal 

 regions, diverticuli of the abdominal cavity, located in the inguinal tracts, 

 where they form the special reservoirs to be hereafter described as the 

 vaginal sheaths (or canals). 



G. The lateral regions (right and left lumbar of Man) are limited : in front, 

 by the costal attachments of the diaphragm ; behind, by the entrance to the 

 pelvic cavity ; above, by the superior border of the small oblique muscle ; 

 below, by the interval comprised between the inferior border of that muscle 

 and the external border of the great rectus muscle. The designation of 

 hypochondriac is given to the subregion which corresponds to the cartila- 

 ginous circle of the false ribs. The flank is that section covered by the 

 muscular portion of the small oblique muscle. 



D. The anterior, or diaphragmatic region, comprises the cavity formed by 

 the posterior face of the diaphragm. Like that muscle, it is divided into 

 two regions, a central and peripheral. 



E. The posterior, or pelvic region, is a special diverticulum of the abdomen 

 described as the pelvic cavity. It is bounded, above, by the sacrum ; below, 

 by the superior face of the pubes, the ischia, and the internal obturator 

 muscle ; on the sides, by the constricted portions of the ossa innominata 

 and the sacro-ischiatic ligaments. The entrance to this diverticulum is 

 situated above the pubes, and is of an oval form. Posteriorly, it is narrower, 

 and is traversed by the rectum and the genito-urinary organs, which open 

 externally. 



THE PERITONEUM. The abdominal cavity is covered, internally, by a 

 serous membrane, the peritoneum, which will now be briefly described. 



Like all the splanchnic serous membranes, the peritoneum is composed ot 

 a parietal and a visceral layer, which together form a closed sac, so arranged 

 that the organs contained in the abdomen are situated external to this sac. 

 The adjoining theoretical figure (180), representing a transverse section of the 

 abdominal cavity, will show at a glance this arrangement. Let A represent 

 the section of the small intestines floating at liberty in the interior of the 



