Intercostal Nerves 151 



and thus it comes about that in inflammation of the upper part of 

 that membrane pain is sometimes felt along the inner side of the 

 arm. 



The lower intercostal nerves, having reached the limit of the space, 

 pass onwards between the internal oblique and transversalis to the 

 sheath of the rectus, and, having pierced it and the rectus, appear as 

 anterior cutaneous nerves near the linea alba. The lower intercostal 

 nerves supply the oblique, the transverse, and the straight muscles of 

 the abdomen. 



Thus, pain over the upper part of the abdomen may be due to 

 pleurisy, to pressure of thoracic tumours or of pleural collections of 

 fluid, to caries of the lower dorsal vertebrae, or to disease of the cord 

 above the lumbar enlargement. 



The anterior division of the last dorsal nerve runs below the last 

 rib, in company with the first lumbar artery, in front of the quadratus 

 lumborum, and gains eventually the space between the transversalis 

 and the obliquus internus. Its peripheral branches (anterior cuta- 

 neous) end about half-way between the umbilicus and pubes. The 

 region of the ' pit of the stomach ' is supplied by the endings of the 

 sixth and seventh nerves. The nerve-supply of any part of the side 

 or front of the thoracic or thoracico-abdominal region is indicated by 

 continuing forward the lines of the intercostal spaces, and seeing which 

 of them runs into that particular area. 



When a patient complains oft. pains over the upper part of the front 

 of the chest, the surgeon must not satisfy himself with tracing his finger 

 along the upper intercostal spaces and with examining the higher 

 dorsal vertebrae, but must carry his investigations also into the middle of 

 the neck, as the third and fourth cervical nerves (p. 145) furnish cuta- 

 neous branches to that neighbourhood as well as the dorsal nerves. 



The lateral cutaneous branch of the last dorsal comes over the iliac 

 crest, through the internal and external obliques, and supplies the skin 

 of the fore part of the buttock, as far as the great trochanter. 



Neuralgia in an intercostal nerve may be due to inflammation in 

 its fibrous elements, and may then be followed by a crop of vesicles 

 in the area of skin supplied by it. The disease is called herpes zoster 

 (fa>(rn;p, belt] or shingles (cingulum, girdle\ names which well describe 

 the arrangement of the eruption. 



The posterior divisions of the dorsal nerves give off internal and 

 external branches. The internal branches of the upper six nerves 

 supply the erector spinas, and then send cutaneous twigs through the 

 trapezius ; all the external branches also give muscular twigs, but, in 

 addition, the lower six send twigs through to the skin of the infra- 

 scapular region. 



According to Professor Griffith, the posterior branches descend 

 obliquely for the depth of several vertebras before ending in the skin, 

 and so it comes about that the line of herpes zoster is transverse and 



