1044 



THE ORGANS OF DIGESTION. 



Laterally : 



Fat of ischio-rectal fossae ; 

 Levatores ani muscles. 



The other ways of describing the rectum (page 1038) only affect its method 

 of subdivision. 



Treves describes the two lower parts of the rectum and includes the first in 

 the sigmoid flexure. This is doubtless an improvement on the old method. He 

 says : l " The segments of the gut termed the sigmoid flexure and first part of 

 the rectum form together a single loop which cannot be divided into parts. This 

 loop begins where the descending colon ends, and ends at the spot where the 

 mesorectum ceases opposite the third piece of the sacrum. This loop when un- 

 folded describes a figure that may be compared to the capital omega " (Fig. 661). 



" The average length of this adult omega loop is seventeen and a half inches, 

 varying from six to twenty-seven. Its normal position is not in the left iliac 

 fossa, but in the pelvis. Its most usual arrangement is this : the descending colon 

 ends just at the outer border of the Psoas. The gut crosses the muscle at right 



Psoas 



Jb- Internal iliac 

 vessels 



FIG. 661. Omega loop of sigmoid flexure. (Treves.) 



Bladder 

 FIG. 662. Usual course of the omega loop. (Treves.) 



angles and descends vertically along the left pelvic wall, and may at once reach 

 the pelvic floor. It then passes more or less horizontally and transversely across 

 the pelvis from left to right and commonly comes into contact with the right pelvic 

 wall. Here it is bent upon itself, and passing once more toward the left reaches 

 the middle line and descends to the anus " (Fig. 662). 



The line of attachment of the mesocolon that fastens the omega loop is as 

 follows (Fig. 661): " It crosses the Psoas at a right angle, and then takes a slight 

 curve upward so as to pass over the iliac vessels about at their bifurcation. The 

 curve ends at the point Jf, which is most frequently at the bifurcation of the 

 vessels. From here the line of attachment proceeds vertically down to termi- 

 nate at N. Its course is to the left of the middle line, while its ending will be 

 upon that line. At the point X the mesocolon is folded a little, and here there 

 arises that part of the membrane which goes to the summit of the loop Y. Here 

 the mesocolon attains its greatest length, and at this spot the sigmoid artery 

 enters. The average length of the mesocolon is over the Psoas one and a half 

 inches ; at the point X three and a half inches ; on the sacrum one and three- 

 fourths inches. The distance between the ends of the loop M and N is three 

 inches." 



1 Hunterian Lectures, 1885: "The Anatomy of the Intestinal Canal and Peritoneum in Man." 



