THE ABDOMEN, INTERIOR. 505 



In rectal operations it is important to know how far the 

 peritoneum is from the seat of operation. Posteriorly the 

 peritoneum is at a distance of five inches, anteriorly of three 

 inches from the anus. The second portion, see page 421. 



TJie Surface Area of the Intestines. The abdomen is 

 divided into regions as indicated, page 435. 



The caecum occupies the right lumbar region ; it is 

 usually located in the text-books in the inguinal region, 

 but this places it too low ; it may reach to, but not often 

 below, the lower horizontal line (see page 435), and lying in 

 the upper portion of the right iliac fossa. 



The appendix joins the caecum at a point on the ilio- 

 umbilical line two and one-half inches from the iliac end, or 

 where this line is crossed by the right vertical. 



The ileocaecal valve is three inches from the iliac spine on 

 the ilio-umbilical line. 



The ascending colon reaches upward through the right 

 lumbar region to a little above the anterior liver border. 



The hepatic and splenic flexures are situated in the right 

 and left lumbar and hypochondriac regions ; when the upper 

 horizontal line is drawn between the tips of the tenth ribs, 

 these flexures may not reach above this line, if so they lie 

 within the lumbar regions. Between these flexures the 

 transverse colon extends, looping downward to just above 

 the umbilicus. 



The descending colon occupies the left lumbar region, 

 while the omega loop describes almost a circle from the 

 left iliac fossa through the lower left portion of the umbili- 

 cal region into the pelvis, to terminate in the rectum 

 behind the middle line. 



The operation of introducing a high rectal tube is some- 

 times described. If the rectum and omega loop is exam- 

 ined it will be seen that it is impossible to pass any tube 



