2^EEVES OF THE THORAX. 597 



3, the nerre of "VVrisberg ; 4, the intercostal nerves continued forwards to 4', their ante- 

 rior cutaneous twigs ; 5, the lateral cutaneous branches of these nerves ; 6, cutaneous 

 branch of the last dorsal spinal nerve ; 7, the il'ac twig of the ilio-hypogastric branch 

 of the first lumbar nerve ; 8, termination of the ilio-hypogastric ; 9, the ilio-inguinal ; 

 10, the middle cutaneous of the thigh, 



greater pectoral, and end in the integument of the breast, receiving the 

 name of the anterior cutaneous nerves of the tliorax. 



A.t the anterior part of the chest some of the muscular twig-s cross the car- 

 tilages of the ribs, passing from one intercostal space to another. 



(a) The lateral cutaneous nerves of thie tliorax inerce the external inter- 

 costal and serratus magnus muscles, in a line a little behind the pectoral border 

 of the axilla. The first intercostal usually gives no lateral branch or only a 

 slender twig to the axilla, but, when that of the second nerve is miusually small, 

 it is supplemented by that of the first. The branch from the second intercostal 

 is named intercosto-humeral. and requires separate description. Each of the 

 remaining lateral cutaneous nerves divides into two branches, which reach the 

 integument at a short distance from each other, and are named anterior and 

 posterior. 



The anterior hranehes are continued forwards over the border of the gi*eat 

 pectoral muscle. Several reach the mammary gland and the nipple ; and from 

 the lower nerves twigs are supplied to the digitations of the external oblique 

 muscle of the abdomen. 



The pofitcrior branches turn backwards to the integument over the scapula and 

 the latissimus dorsi muscle. The branch from the thii-d nerve ramifies in the 

 axilla, and a few filaments reach the ai-m. 



The inicrcosto-laimcral ner\-e. the lateral cutaneous branch of the second inter- 

 costal nei"ve, corresponds with the posterior of the two divisions of the succeeding 

 lateral [cutaneous branches, the anterior being commonly wanting. It crosses 

 the axillary space to reach the arm, and is connected in the axilla with an offset 

 of the nerve of Wrisberg. Penetrating the fascia it becomes subcutaneous, and 

 ramifies ia the integument of the upper half of the arm, on the inner and pos- 

 terior aspect ; a few filaments reach the integument over the scapula. The 

 branches of this nerve cross over the internal cutaneous offset of the musculo- 

 spiral, and a communication is established between the two nerves. The size of 

 the intercosto-humeral nerve, and the extent of its distribution, are in tlie 

 inverse proportion to the size of the other cutaneous nerves of the upper arm, 

 especially the nerve of "Wrisberg. 



(b) The anterior cutaneous nerves of the thorax, which are the terminal 

 twigs of the intercostal nerves, are reflected outwards in the integument over the 

 great pectoral muscle. The branch from the second nerve is connected with the 

 superclavicular and the lateral cutaneous nerves ; those from the third and f omth 

 nerves are distributed to the mammary gland. 



LOWER OR ABDOMINAL INTERCOSTAL NERVES. 



The lower intercostal nerves are continued from the anterior ends of 

 the intercostal spaces, between the internal oblique and the transverse 

 muscle of the abdomen, to the outer edge of the rectus. Perforating 

 the sheath, they enter the substance of that muscle, and afterwards 

 terminate in small cutaneous branches (anterior cutaneous). 



(rt) The lateral cutaneous nerves of the abdomen pass to the integument 

 through the external Intercostal and external oblique muscles, in a line with the 

 corresponding nerves on the thorax, and divide in the same manner into anterior 

 and posterior branches. 



The anterior branches are the larger, and are directed inwards in the super- 

 ficial fascia, with small cutaneous arteries, nearly to the edge of the rectus 

 muscle. 



