234 THE DIGESTIVE SYSTEM 



referring the individual viscera to the surface of the body. 

 The three regions which occupy the median plane are termed 

 from above downwards, the epigastric, the umbilical and the 

 hypogastric regions respectively. 



The transpyloric plane, though not utilised in the sub- 

 division of the abdominal cavity, is extremely useful in con- 

 nexion with the relations of viscera to the surface. It passes 

 horizontally through the body and bisects the line which joins 

 the upper border of the manubrium sterni to the pubic 

 symphysis. As a rule, it cuts the vertebral column opposite 

 the lower border of the first lumbar vertebra and lies about 

 \\ inches above the subcostal plane. 



These regions and planes will be frequently referred to in 

 the description of the various abdominal viscera. 



THE PERITONEUM 



The Peritoneum is the most extensive serous membrane in 

 the body. In the male, it forms a completely closed sac, but, 

 in the female, the peritoneal cavity communicates with the 

 uterine (Fallopian) tube and so indirectly with the exterior 

 through the ostium abdominale (p. 396). 



It is customary, as in the case of the pleura (p. 341), to 

 refer to visceral and parietal layers, but it must be remembered 

 that certain viscera, e.g. the pancreas, kidneys, etc., are retro- 

 peritoneal, and that they are partially covered on their anterior 

 surfaces by the peritoneum of the posterior abdominal wall. 

 The arrangement of the peritoneum in relation to the abdominal 

 viscera is best comprehended by the study of sagittal and 

 transverse sections through the abdominal cavity. 



A sagittal section in the median plane passes, successively, 

 through the liver, the stomach, the transverse colon and coils 

 of the small intestine (Fig. 88), and, on the posterior abdominal 

 wall, it passes through the pancreas and the third part of the 

 duodenum. When the cut surface of such a section is 

 examined (Fig. 88), it is found that the layer of peritoneum on 



