



THE PERITONEUM 1149 



further subdivided into three regions by the two sagittal planes, which are indi- 

 cated on the surface by lines drawn vertically through points half-way between 

 the anterior superior iliac spines and the symphysis pubis. 1 



The middle region of the upper zone is called the epigastric ; and the two lateral 

 regions, the right and left hypochondriac. The central region of the middle zone 

 is the umbilical; and the two lateral regions, the right and left lumbar. The middle 

 region of the lower zone is the hypogastric or pubic region; and the lateral regions 

 are the right and left iliac or inguinal (Fig. 1034). 



The pelvis is that portion of the abdominal cavity which lies below and behind 

 a plane passing through the promontory of the sacrum, linese terminales of the 

 hip bones, and the pubic crests. It is bounded behind by the sacrum, coccyx, 

 Piriformes, and the sacrospinous and sacrotuberous ligaments; in front and 

 laterally by the pubes and ischia and Obturatores interni; above it communicates 

 with the abdomen proper; below it is closed by the Levatores ani and Coccygei and 

 the urogenital diaphragm. The pelvis contains the urinary bladder, the sigmoid 

 colon and rectum, a few coils of the small intestine, and some of the generative 

 organs. 



When the anterior abdominal wall is removed, the viscera are partly exposed 

 as follows: above and to the right side is the liver, situated chiefly under the shelter 

 of the right ribs and their cartilages, but extending across the middle line and reach- 

 ing for some distance below the level of the xiphoid process. To the left of the liver 

 is the stomach, from the lower border, of which an apron-like fold of peritoneum, 

 the greater omentum, descends for a varying distance, and obscures, to a greater 

 or lesser extent, the other viscera. Below it, however, some of the coils of the small 

 intestine can generally be seen, while in the right and left iliac regions respectively 

 the cecum and the iliac colon are partly exposed. The bladder occupies the ante- 

 rior part of the pelvis, and, if distended, will project above the symphysis pubis; 

 the rectum lies in the concavity of the sacrum, but is usually obscured by the coils 

 of the small intestine. The sigmoid colon lies between the rectum and the bladder. 



When the stomach is followed from left to right it is seen to be continuous with 

 the first part of the small intestine, or duodenum, the point of continuity being 

 marked by a thickened ring which indicates the position of the pyloric valve. 

 The duodenum passes toward the under surface of the liver, and then, curving 

 downward, is lost to sight. If, however, the greater omentum be thrown upward 

 over the chest, the inferior part of the duodenum will be observed passing across 

 the vertebral column toward the left side, where it becomes continuous with the 

 coils of the jejunum and ileum. These measure some 6 meters in length, and if 

 followed downward the ileum will be seen to end in the right iliac fossa by opening 

 into the cecum, the commencement of the large intestine. From the cecum the 

 large intestine takes an arched course, passing at first upward on the right side, 

 then across the middle line and downward on the left side, and forming respectively 

 the ascending transverse, and descending parts of the colon. In the pelvis it 

 assumes the form of a loop, the sigmoid colon, and ends in the rectum. 



The spleen lies behind the stomach in the left hypochondriac region, and may 

 be in part exposed by pulling the stomach over toward the right side. 



The glistening appearance of the deep surface of the abdominal wall and of the 

 surfaces of the exposed viscera is due to the fact that the former is lined, and the 

 latter are more or less completely covered, by a serous membrane, the peritoneum. 



The Peritoneum (Tunica Serosa). 



The peritoneum is the largest serous membrane in the body, and consists, in the 

 male, of a closed sac, a part of which is applied against the abdominal parietes, 



'Journal of Anatomy and Physiology, vols. xxxiii, xxxiv, xxxv. 



