334 THE ABDOMEN AND PELVIS 



anastomose with any other artery, and therefore, when it 

 becomes kinked or obstructed,, the blood-supply of the process 

 is entirely cut off and gangrene ensues. 



Intussusception. A condition of incipient intussusception 

 is always present on account of the invagination of the circular 

 muscular coat into the segments of the colic (ileo-csecal) valve. 

 This constitutes a predisposition to ileo-ccecal intussusception ,but 

 the condition can only occur when the ascending colon possesses 

 a mesentery. The frequency of its incidence during the first year 

 is explained by the fact that the relative disproportion in calibre 

 between the large and small intestine is greatest at that period. 



It is said that if a wave of peristalsis passes up the caecum 

 just as one ends on the ileum, the colic valve, which is at that 

 moment projected furthest within the lumen of the caecum, is 

 seized by the contracting caecum and squeezed upwards along 

 the ascending colon. When the angle at which the ileum joins 

 the colon is greater than 90, intussusception occurs more readily. 



In this variety the colic valve forms the apex of the 

 intussusceptum, and as it passes along the large intestine, the 

 caecum, vermiform process and ascending colon are dragged in 

 together with the ileum and its mesentery. Finally, the colic 

 valve may appear at the anus. 



In the ileo-colic variety the intussusception begins in the 

 ileum, usually near its terminal portion. The part of the gut 

 which constitutes the starting-point of the condition remains 

 at the apex of the intussusceptum (Fitzwilliams), both before 

 and after it has passed through the colic valve. If the ascending 

 colon possesses a mesentery, the subsequent course of events is 

 the same as in the ileo-caecal variety. If the ascending colon 

 has no mesentery, the intussusception stops at the valve. 



The Ascending Colon runs upwards on the iliacus, the 

 quadratus lumborum, and the lower pole of the right kidney 

 (Fig. 88) ; it is separated from both muscles by their fascia 

 and from the kidney by the peri-nephric fascia. It separates 

 the right para-colic gutter from the right infra-colic compartment, 

 and is bound to the posterior abdominal wall by the peritoneum, 

 which clothes its anterior, medial, and lateral surfaces. 

 Occasionally the right margin of the greater omentum is fused 

 with the peritoneal covering of the ascending colon. In that 

 case the right half of the transverse colon is often closely related 

 to the ascending colon, forming what has been termed the 

 " double-barrelled gun " arrangement (Fig. 105). 



