ABDOMINAL CAVITY 333 



ileum is to some extent prevented, but it must be noted that 

 the circular muscle layer at the end of the ileum plays the 

 part of a definite sphincter muscle. 



The position of the ileo-caecal orifice is marked, on the 

 anterior surface of the abdomen, by the lower medial angle 

 between the intertubercular and the right lateral lines. About 

 25 mm. (i inch) below the ileo-caecal orifice, and on a posterior 

 plane, is the orifice of the vermiform process, which may be 

 quite open, or it may be partly guarded by a semilunar fold 

 of mucous membrane, the valve of the vermiform process. 



Colon Ascendens. The ascending colon passes upwards 

 from the caecum, through the upper part of the right iliac 

 fossa, and through the right lumbar region to the right flexure 

 of the colon in the right hypochondriac region. It varies from 

 about 12.5 to 20 cm. (five to eight inches) in length. It is 

 covered in front and at the sides by peritoneum, which binds 

 it to the posterior wall of the abdomen. Occasionally it is 

 attached to the posterior abdominal wall by an ascending 

 meso-colon. Anteriorly, it is either in contact with the anterior 

 wall of the abdomen, or it is separated from the abdominaf 

 wall by coils of small intestine and the right free margin ol 

 the greater omentum. 



Dissection. The peritoneum along the medial border of 

 the ascending colon has already been divided. Now divide 

 the peritoneum along the lateral border ; then turn the caecum 

 and the ascending colon upwards, and remove the fatty areolar 

 tissue which lies behind the colon. Note that the ascending 

 colon lies anterior to the upper part of the right iliacus muscle, 

 the crest of the right ilium, and, above the crest, in front of the 

 fascia covering the right quadratus lumborum and the medial 

 part of the aponeurosis of the origin of the right transversus 

 abdominis. It is separated from the quadratus lumborum, 

 however, not only by the anterior lamella of the lumbar fascia, 

 but also by three nerves the last thoracic, the ilio-hypogastric 

 and ilio- inguinal. It is possible that the dissector will not 

 be able to display the last thoracic nerve at this stage of the 

 dissection. 



Flexura Coli Dextra (O.T. The Hepatic Flexure). The 



right flexure of the colon lies in the right hypochondrium, 

 below and somewhat behind the anterior part of the lower 

 surface of the right lobe of the liver, to the right of the gall- 

 bladder, and in front of the lower part of the right kidney. 

 It is covered by peritoneum except on its posterior surface, 

 which is attached to the kidney by loose areolar tissue. 



Colon Transversum. The transverse colon extends first 



