504 A MANUAL OF ANA TOMY. 



with a sort of sphincter, formed by an increase in the circular 

 fibres, and a narrowing in the calibre of the bowel. The 

 omega loop lies normally within the pelvic cavity. The loop 

 has a distinct mesentery and is freely movable, being sur- 

 rounded almost entirely by peritoneum. 



The attachment of the omega mesentery crosses the 

 psoas at right angles, the iliac vessels at their bifurcation, 

 and curves downward into the pelvis toward the right so as 

 to reach the median line. This line of attachment meas- 

 ures about three and one-half inches, and the mesentery is 

 about the same in width. 



Relations. With the small intestines in front and to the 

 inner side. With the caecum and vermiform appendix (if 

 distended) on the right. With the iliacus and psoas, genito- 

 crural nerve, iliac vessels, first portion of sacrum behind. 

 Below it rests upon the bladder and rectum and in the 

 female, upon the uterus. 



The rectum (Figs, no, in), is the last portion of the 

 large intestine from the end of the omega loop at the third 

 portion of the sacrum to the anus, and measures about 

 five inches. It may conveniently be described in two por- 

 tions. The first portion three and one-half inches, from the 

 third portion of the sacrum to the tip of the coccyx. This 

 part of the rectum is covered by peritoneum only upon its 

 front and at the very beginning. In front of this portion 

 are the bladder, seminal vesicle, trigone, posterior surface 

 of the prostate. In the female, with the posterior surface 

 of the cervix of the uterus and upper part of the vagina. 

 Behind, it rests upon the lower part of the sacrum and the 

 coccyx conforming to the sacral curve. 



The peritoneum is reflected from the rectum to the 

 bladder or the vagina, and in the bottom of this reflection 

 is the rectovesical or rectovaginal fossa. 



