276 THE DIGESTIVE SYSTEM 



the caput Medusae. This condition must be compared 

 with and distinguished from the somewhat similar condition 

 induced by obstruction of the inferior vena cava (p. 316). 

 In portal obstruction^ the blood-stream flows away from the 

 umbilicus. Some of the veins run upwards and laterally to 

 end ultimately in the superior vena cava, while others pass 

 downwards and laterally to join the femoral vein and so end 

 in the inferior vena cava. The presence of the caput 

 Medusa not only is diagnostic of portal obstruction but it 

 is diagnostic of portal obstruction within the liver itself, for the 

 upper end of the para-umbilical vein is connected to the left 

 branch of the portal vein and, therefore, cannot be involved 

 when the obstruction occurs below the porta hepatis (trans- 

 verse fissure of the liver). 



THE LARGE INTESTINE 



The Caecum. The caecum is that part of the large intestine 

 which lies below the termination of the ileum (Fig. 101). It 

 forms a blind sac, about 2\ inches long and 3 inches wide, 

 which occupies the right iliac fossa, and it can be mapped out 

 on the surface in the area below the inter-tubercular plane and 

 to the lateral side of the right lateral plane (Fig. 101). Under 

 normal conditions, the caecum is completely invested by peri- 

 toneum, and therefore enjoys a certain degree of mobility. 

 The peritoneum on its anterior and lateral aspects is con- 

 tinuous with the corresponding covering of the ascending colon, 

 but the peritoneum on its posterior aspect is reflected back- 

 wards from its upper end to the iliac fossa. 



So long as its muscular wall is healthy, the caecum does not 

 extend beyond the right iliac fossa, but when the wall loses its 

 tone, the caecum tends to sag downwards and medially over the 

 brim of the pelvis. Lane suggests that this latter condition is 

 by no means uncommon and that thickened bands, which pass 

 upwards and laterally and upwards and medially, respectively, 

 from the upper end of the caecum, are developed in an 



