236 HUMAN ANATOMY. 



to that of the large and small intestines respectively, being cov- 

 ered with villi on the side toward the ileum, and being destitute 

 of villi, and containing numerous tubular glands or crypts of 

 Lieberkiihn, on the side toward the caecum. This difference oc- 

 curs abruptly at the free margin of the valves. 



THE COLON consists of four portions ascending, transverse, 

 and descending colon, and sigmoid flexure : 



The ascending portion begins opposite the ileo-ca?cal valve, 

 ascends through the right lumbar and hypochondriac regions, and 

 terminates beneath the under surface of the liver at the hepatic 

 flexure in the transverse portion. Its posterior surface is desti- 

 tute of peritoneum, and is attached to the quadratus lumborum 

 muscle by loose areolar tissue. 



The transverse portion, or transverse arch of the colon, 

 passes from the hepatic flexure, through the adjoining portions 

 of the epigastric and umbilical regions, to terminate at the 

 splenic flexure in the descending portion. It is attached by the 

 transverse mesocolon, and is the most movable portion of the 

 colon. 



The descending portion begins at the splenic flexure, de- 

 scends through the left lumbar and iliac regions to terminate 

 in the sigmoid flexure. Like the ascending colon, its posterior 

 surface is destitute of peritoneum. 



The sigmoid flexure (omega loop) is a narrow, twisted por- 

 tion of the colon, occupying the left iliac fossa, between the 

 descending portion of the colon and the rectum. It is held in 

 position by the sigmoid mesocolon. 



THE RECTUM the terminal portion extends from the sig- 

 moid flexure to the anus. It is from six to eight inches in 

 length, not sacculated, but club-shaped, with its large extremity 

 downward, and consists of three portions the upper, middle, and 

 lower : 



The upper portion, about four inches in length, rests upon 

 the sacral plexus of nerves and the pyrif ormis muscle ; 



The middle portion, about three inches, is in relation in 

 the male with the bladder, prostate gland, and vesiculas seminalis ; 

 in the female with the uterus and vagina, being adherent to 

 the latter; 



The lower portion, about one and one-quarter inches, turns 

 backward and terminates in the anus. It is supported by the 

 levator ani muscle, and is surrounded by the internal and external 

 sphincters of the anus. 



The structure of the large intestine consists of four coats 

 serous, muscular, cellular, and mucous : 



The serous coat, derived from the peritoneum, invests com- 

 pletely the transverse portion and upper portion of the rectum, 



