THE INTESTINES 



1377 



blind extremity of the colon lying below the horizontal level of the ileo-caecal 

 valve, is approximately 6.2 cm. (2| in.) in both vertical and transverse diameters, 

 though its size varies much ^vith the degree of distention. It lies usually in 

 contact with the anterior abdominal wall above the lateral half of the inguinal 

 ligament. The orifice of the appendix (vermiform process) lies some 2 cm. below 

 the ileo-ctecal valve. The csecum is completely covered by peritoneum as a 

 rule, though exceptionally its posterior surface is bound down in the right iliac 

 fossa. 



The axial rotation of the midgut and descent of the csecum that normally take place during 

 intra-uterine life (p. 1168) are occasionally not completed, with the result that the caecum and 

 appendix may be found above and to the left of the umbihcus, or less uncommonly just below 



Fig. 1109. — Blood-vessels of the Ileo-c.eal Region. (From Kelly). 



the right lobe of the liver (3 per cent., Alglave), when an attack of appendicitis may simulate 

 inflammation of the gall-bladder. On the other hand certain cases occur in which the caecum 

 descends unusually far, proceeding downward and medially until it becomes a pelvic organ 

 whenever the bladder and rectum are empty. This pelvic position of the caecum is found in 

 10 per cent, of infants (G. M. Smith).* 



In the commonest form of intussusception, the ileo-caecal valve and lower ileum are pro- 

 lap.sed into the colon and carried down by the force of peristalsis toward the anus. The valve 

 in these cases forms the apex of the intussusceptum, however far it travels. 



* Anat. Record, vol. 5, 1911, p. 549. 



87 



