242 THE ABDOMEN AND PELVIS 



the abdominal wall. Their obliquity can be appreciated if the 

 course of the eighth intercostal nerve is examined. Posteriorly, 

 it is placed at the level of the inferior angle of the scapula, but 

 anteriorly it ends midway between the xiphoid process and the 

 umbilicus. The lateral cutaneous branches descend under cover 

 of the fascia before they come to the surface, and so, despite the 

 oblique course of the main trunks, the terminal branches supply 

 areas of skin, which are almost horizontal (Fig. 72). 



The skin of the posterior abdominal wall is supplied by the 

 posterior rami (primary divisions) of the lower thoracic and upper 

 lumbar nerves (L. i, 2, and 3). (Fig. 3). 



These incline downwards in the fascia, and become cutaneous 

 on the same horizontal plane as the lateral and anterior branches. 



In Herpes Zoster the affected areas do not map out the 

 course of a thoracic nerve, but the terminations of its cutaneous 

 branches. They therefore form horizontal strips round the 

 body, and they correspond exactly to the areas in which the 

 " girdle pains " are experienced in locomotor ataxia. 



Referred Pain. The anterior rami (ant. prim, divisions) 

 of the thoracic and of the first (and sometimes second) 

 lumbar nerves are connected to the corresponding ganglia of 

 the sympathetic by both white and grey rami communicantes 

 (p. 125). The nerve-supply to the abdominal viscera is derived 

 from the lower eight thoracic and the first lumbar segments 

 and, consequently, afferent impulses from the viscera reach 

 the same segments in the spinal medulla (cord) as do the afferent 

 impulses from the skin of the abdominal wall. In pathological 

 conditions the afferent impulses from the viscera may become 

 so altered, either in strength or character, as to overflow those 

 cells for which they were originally intended, and stimulate 

 those neighbouring cells which are accustomed to receive 

 impulses from the skin of the abdominal wall (Fig. 73). When 

 the stimuli from these latter cells reach the brain, they are 

 interpreted as painful sensations affecting the skin area supplied 

 by the segment of the spinal medulla which is involved. Pain 

 of this variety, which may be felt in a different region from the 

 viscus at fault, is spoken of as referred pain, and the whole reflex 

 is called the " viscero- sensory reflex" (Mackenzie). The areas 

 in which referred pain may be felt in pathological conditions of 

 the various viscera are dealt with under each individual organ 

 (pp. 298, 312, etc.). 



The Superficial Veins of the abdominal wall may be divided 



