278 THE DIGESTIVE SYSTEM 



DEVELOPMENT OF THE CECUM AND VERMIFORM PROCESS. 

 During the third week a localised dilatation appears on the anti- 

 mesenteric border of the hind-gut (p. 286). After a time, the 

 calibre of the proximal part of the dilatation increases in the 

 same proportion as the rest of the intestinal tube, but the distal 

 part remains relatively much smaller in diameter, although it 

 continues to increase in length. This is the first sign of the 

 formation of the vermiform process, which at first springs from 

 the apex of the caecum. After birth, the lateral wall of the 

 caecum grows much more rapidly than the medial wall, so that 

 the vermiform process in the adult springs from the medial 

 wall of the caecum and not from its apex. 



During the development of the caecum, the intestinal tube 

 increases in length and forms a U-shaped loop, which is sus- 

 pended from the posterior abdominal wall by a dorsal mesen- 

 tery. The caecum lies on the distal limb of the L). The loop 

 becomes rotated counter-clockwise through 180, so that the 

 distal limb of the I) is carried across the anterior surface of 

 the proximal limb. After this rotation of the gut has taken 

 place, the caecum lies in contact with the lower surface of the 

 right lobe of the liver. At birth, however, it is found normally 

 in the right iliac fossa, but, not infrequently, the caecum and 

 vermiform process are found at operations in the infra-hepatic 

 position. 



The NERVE-SUPPLY OF THE C/ECUM AND THE VERMIFORM 

 PROCESS is derived from a number of sympathetic nerves 

 which accompany their arteries of supply. These nerves have 

 their centres in the region of the eleventh thoracic segment of 

 the spinal medulla. 



In the early stages of appendicitis the pain is usually 

 experienced in the median plane, at or just below the umbili- 

 cus, and it is perfectly clear that we are here dealing with an 

 example of the viscero-sensory reflex (p. 192). The abnormal 

 afferent stimuli may "overflow" from the eleventh segment 

 and affect the adjoining segments. As a result, the pain is not 

 confined to the area supplied by the eleventh intercostal nerve, 



