1222 



THE DIGESTIVE SYSTEM. 



blends with, the parietal peritoneum on the posterior abdominal wall, and is completely lost as 

 a rule. The persistence of this mesentery, in a greater or less degree, explains the occasional 

 presence of a descending mesocolon in the adult. 



Iliac Colon. This corresponds to the portion of the "sigmoid flexure" which 

 lies in the iliac fossa, and it has no mesentery. It is the direct continuation of 

 the descending colon, with which it agrees in every detail, except as regards its 

 relations. Beginning at the crest of the ilium, it passes downwards and somewhat 

 medially, lying in front of the iliacus muscle. A little way above the inguinal 

 ligament it turns medially over the psoas major, and ends at the medial border of 

 this muscle by dipping into the pelvis and becoming the pelvic colon (Fig. 958). It 

 usually measures about 5 or 6 inches (12'5 to 15 cm.) in length, but it varies 

 considerably in this respect. 



Fibro-cartilage between 

 4th and 5th lumbar vertebrae 



V. iliaca communis 

 Pelvic mesocolon 





A. iliaca communis 



Commencement of iliac colon 

 Sacculation 



V. hypo- 

 gastrica 



A. hypo- 

 gastrica 



Pararectal 



Appendix 

 epiploica' 



Tsenia anterior 



V. iliaca externa 



A. umbilicalis dextra , 

 Median umbilical ligament artery (urachus) 



A. umbilicalis sinistra 



Urinary bladder, superior surface 

 A. umbilicalis sinistra 



FIG. 958. THE ILIAC AND PELVIC COLON IN SITU. 



Relations. Posteriorly, it lies upon, and, as a rule, is connected by areolar 

 tissue to, the front of the ilio-psoas muscle. It also crosses the left ureter, the 

 left internal spermatic vessels, and the femoral nerve. Anteriorly, it is usually 

 covered by coils of smaU intestine, which hide it from view ; but when distended, 

 or when it occupies a lower position than usual, it comes into direct contact, wit 

 the anterior abdominal waU. As a rule (90 per cent, of bodies Jonnesco), it 

 covered with peritoneum only on its sides and anterior surface. Occasionally 

 (10 per cent, of cases) it is completely covered, has a short mesentery (1 inch, 2 

 3 cm.), and is slightly movable. 



In its course it passes. down over the iliac fossa near its middle, generally forming a curve 

 with its concavity directed medially and upwards, and having reached a point 1| or 2 inch < 

 to 5 cm.) above the inguinal ligament, it turns medially across the psoas major towards the pel 

 cavity. Occasionally the iliac colon occupies a lower position than this, and runs along tl 

 surface of the inguinal ligament, immediately behind the anterior abdominal wall. 



Pelvic Colon. The pelvic colon is a large coil of intestine, which begins at the 

 medial border of the left psoas major muscle, where it is continuous with the il 



