I3i8 HUMAN ANATOMY. 



2. The cutaneous branches are larger than the muscular and consist of two 

 sets : (a) the lateral cutayieous and i^b) the anterior cutaneous. 



a. The lateral cutaneous branches (rr. cutanei laterales) consist of two series, an upper 

 and a lower, the former originating from the first to the sixth and the latter from the sixth to the 

 twelfth thoracic nerves. Those of the upper series pierce the external intercostal muscles and 

 those of the lower the external oblique in a line situated midway between the mammary and 

 mid-axillary lines. The upper seven pass between the digitations of the serratus magnus and the 

 lower between the digitations of the latissimus dorsi and the external oblique. The one arising 

 from the twelfth pierces the musculature of the external oblique. Each lateral cutaneous nerve 

 divides into {aa) an anterior and {bb) a posterior branch (Fig. 1083). 



aa. The posterior branches (rr. posteriores) are smaller than the anterior. They wind 

 around the edge of the latissimus dorsi and supply the integument of the lateral area of the 

 trunk as far back as the anterior margin of the region supplied by the posterior primary divi- 

 sions of the thoracic nerves. The branches from the third to the sixth inclusive have fibres 

 which are distributed over the lateral portion of the scapula. 



bb. The anterior branches (rr. anteriores [pectorales et abdominales] ) are of considerably 

 greater size than the posterior. Those from the second to the seventh pass toward the lateral 

 margin of the pectoralis major and supply the integument of this region as far forward as the 

 nipple. Branches (rr. mammarii laterales) from the fourth, fifth, and sixth send filaments to 

 the skin and substance of the mammary gland. Those from the seventh to the eleventh supply 

 the integument of the abdomen as far anterior as the lateral margin of the rectus. The anterior 

 branch from the twelfth has a filament which passes over the iliac crest to the integument of the 

 gluteal region, usually sending a branch as far as the great trochanter. It maintains a more or 

 less even balance with the corresponding branch of the first lumbar nerve, each supplying any 

 deficiency in the other. 



b. The anterior cutaneous branches (rr. cutanei anteriores) are the terminal fibres of the 

 thoracic nerves. Those from the upper six (rr. cutanei pectorales anteriores) pierce the pectoralis 

 major near the lateral margin of the sternum and supply the adjacent integument of the thorax. 

 Filaments (rr. mammarii mediales) are distributed to the skin of the mesial portion of the mam- 

 mary gland. The anterior cutaneous branches from the lower six (rr. cutanei abdominales ante- 

 riores) vary in position. They consist of the terminal filaments which perforate the anterior 

 portion of the rectus sheath at a situation anywhere between the lineae alba and semilunaris. 

 Those from the seventh become superficial near the ensiform cartilage, those from the tenth 

 supply the region of the umbilicus and those from the twelfth are distributed to the area located 

 midway between the umbilicus and the pubic crest (Fig. 1105). 



Practical Considerations. — Of the branches of the thoracic spinal nerves, 

 the anterior or intercostals suffer most frequently from sensory disturbances, and 

 the posterior from motor disturbances. Intercostal neuralgia may result from 

 pressure, as from aneurism or spinal disease, or it may be due to injury. The lower 

 intercostals enter into the supply of both the thoracic and the anterior abdominal 

 walls, the pleura also being supplied by them. Pain referred to the abdominal wall 

 and rigidity of the abdominal muscles may therefore be due to diseases within the 

 chest, as pleurisy. Such diseases in the upper part of the chest may cause pain to 

 extend down the arm along the intercosto-humeral nerve, which is the lateral cuta- 

 neous branch of the second intercostal nerve, or sometimes of the second and third 

 intercostals. The pain of intercostal neuralgias often becomes intense, especially 

 after violent expiratory efforts, as in coughing and sneezing ; not infrequently after 

 the pain ceases, herpes zoster appears in the line of the nerve affected. This may be 

 a trophic disturbance or an extension of the inflammation along the nerve endings 

 to the skin. Mastodynia, or the so-called "irritable breast of Cooper," is due to 

 intercostal neuralgia, and occurs in the female during the child-bearing period. 



The lower intercostal nerves, with the ilio-hypogastric and ilio-inguinal, supply 

 the muscles of the abdominal wall, and are frequently injured by the incisions made 

 in abdominal operations, thus leading to more or less impairment of the muscles sup- 

 plied and favoring the later development of hernia. The incision should therefore, 

 so far as possible, be made in the line of the fibres of the muscles (page 535). 



The intercostal nerves continue their oblique line through the abdominal mus- 

 cles. The pain from Pott's disease is often transferred along the nerves coming from 

 the affected segment of the cord. In this way pain in the abdominal region may 



