THE ABDOMINAL CAVITY 331 



and is guarded by a crescentic fold of mucous membrane. 

 Absence or incompetence of this valve may account for the 

 presence of faecal matter within the process. 



The mesentery of the vermiform process is a triangular fold, 

 which is derived from the left or lower layer of the mesentery of the 

 ileum. It is sometimes shortened and attached to the posterior 

 abdominal wall near the pelvic brim. Occasionally the vermiform 

 process has no mesentery and is entirely retro-peritoneal. 



Although its base is constant in position, in relation to the 

 caecum, the process itself possesses a wide range of movement 

 and may occupy any one of the following situations : 



(1) It may pass upwards and to the left, under cover of the 

 mesentery ; this is known as the splenic position. When the 

 process is retro-peritoneal in this situation, it may lie behind 

 or within the root of the enteric mesentery. 



(2) The vermiform process may pass downwards and to the 

 left, occupying the pelvic position. Inflammatory attacks may 

 give rise to adhesions which connect it to the rectum, bladder, 

 etc. In these cases defsecation or micturition may cause painful 

 symptoms by traction on the adherent vermiform process, and 

 an appendicular abscess may discharge by the rectum or the 

 urethra. When the vermiform process occupies the pelvic 

 position in the female, it is brought into close relationship with 

 the right ovary ; and if signs of inflammation occur, it may be 

 a matter of great difficulty to decide whether the vermiform 

 process or the right ovary is at fault. The relation of the pain 

 to the menstrual period may aid in the diagnosis. Valuable 

 information may be obtained by means of a rectal or a vaginal 

 examination. When the process is retro-peritoneal in the pelvic 

 position, it lies immediately in front of the common iliac vessels 

 and the ureter, and difficulty may be experienced in mobilising 

 it in appendicectomy. 



(3) The vermiform process may pass forwards towards the 

 anterior abdominal wall the anterior position but it can only 

 do so when it possesses a mesentery. If it becomes inflamed 

 in this situation the greater omentum usually surrounds it, 

 and the mass so formed can often be recognised on abdominal 

 palpation. Should an abscess form and rupture, the right infra- 

 colic compartment may be infected (p. 285). 



(4) The vermiform process very frequently takes up a 

 position behind the caecum and then has a varying relation to 

 the peritoneum, (a) It may possess a mesentery and lie free 



