250 THE DIGESTIVE SYSTEM 



and Mackenzie has pointed out that it may be possible to 

 diagnose the site of a gastric ulcer from the position of the 

 areas of cutaneous hyperalgesia, when such are present. 



Gastric referred pain is experienced in the skin areas sup- 

 plied by the fi r th to the eighth thoracic nerves. As a rule 

 the anterior terminal branches of the anterior rami (primary 

 divisions) of these nerves are affected, and the pain is con- 

 sequently referred to the epigastric region, but, at the 

 same time, pain may be experienced over the wide areas of 

 distribution of the lateral branches of the intercostal nerves 

 of the left side. 



When a "focus of irritation" (p. 195) is established in 

 the spinal medulla as the result of a gastric lesion, areas 

 of cutaneous or muscular hyperalgesia may be found on 

 careful examination. In most cases they occur over the 

 upper part of the left rectus abdominis muscle, but they 

 should also be sought for over the left sacro-spinalis (erector 

 spinae). 



An area of cutaneous hyperalgesia, caused by an ulcer near 

 the cardiac end of the stomach, will, theoretically, be situated 

 in the region supplied by the fifth thoracic nerve. On the 

 other hand, a similar area, caused by an ulcer near the pylorus, 

 will be found in the region supplied by the eighth thoracic 

 nerve (Fig. 96), i.e. the lower part of the epigastric region. 

 Ulcers affecting the body of the stomach will give rise to areas 

 of cutaneous hyperalgesia situated in the region supplied by 

 the sixth and seventh thoracic nerves. 



Gastric lesions may give rise also to the viscero-motor reflex 

 (p. 197), and, since the viscero-sensory reflex is usually 

 limited to the areas supplied by the anterior terminal branches 

 of the fifth to the eighth intercostal nerves, it is not surprising 

 to find that the viscero-motor reflex is usually limited to the 

 upper part of the left rectus abdominis, which is supplied by 

 the same nerves. When the lateral branches of these nerves 

 are affected, localised contractions may be found in the upper 

 part of the external oblique muscle, and, when the posterior 



