THE LARGE INTESTINE 279 



but it is also experienced in the areas supplied by the tenth and 

 twelfth thoracic nerves. 



At a later stage, the most acute pain is experienced over 

 M'Burney's point, which lies on the right lateral plane i inch 

 below the intertubercular plane and corresponds to the point 

 where the vermiform process springs from the caecum. At 

 this point, too, there is usually tenderness to deep pressure. 

 It is by no means certain whether these pains are actually felt 

 in the viscus or whether they are felt in the abdominal wall. 

 It is said that in cases of appendicitis, in which the vermi- 

 form process has been subsequently found in the infra-hepatic 

 position, there is no pain or tenderness over M'Burney's 

 point, but these cases are not of frequent occurrence and 

 they have not yet received sufficient attention. 



Cases of appendicitis may give rise to the viscero-motor 

 reflex. This is represented by a localised contraction of the 

 lower parts of the lateral abdominal muscles. It is curious 

 that these areas of muscular contraction usually overlie the 

 affected viscus, for, as already mentioned, the vermiform pro- 

 cess develops in the median plane and its position in the 

 right iliac region is assumed some months after it has received 

 its nerve-supply. 



In pathological lesions of the caecum or the vermiform pro- 

 cess, slight tonic contraction of the right psoas major may 

 occur, as evidenced by slight flexion of the hip-joint. The 

 muscle lies to the medial side of the caecum, and it is possible 

 that it is only affected when its sensory nerves are irritated, 

 e.g., by the presence of an abscess. Mackenzie believes that 

 the condition may be accounted for by the presence of a 

 " focus of irritation " in the spinal medulla, and he suggests 

 that the frequency of micturition, associated with some cases 

 of appendicitis, may be explained in the same way. 



The mucous membrane of the caecum and the vermiform 

 process is richly provided with lymphoid tissue, and these 

 parts of the intestinal canal may, therefore, be the site of 

 ulceration and, sometimes, perforation in typhoid fever* 



