INTERCOSTAL NERVES. 657 



the nerve of Wrisberg; 4, the intercostal nerves continued forwards to 4', their anteiior 

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

 of the last dorsal spinal nerve ; 7, the iliac twig of the ilio-hypogastric branch of the 

 first lumbar nerve ; 8, termination of the ilio-hypogastric ; 9, the ilio-iuguinal ; 10, the 

 middle cutaneous of the thigh. 



the sternum, they cross the internal mammary artery and the fibres of the 

 triangularis sterni muscle. Finally, these nerves pierce the internal inter- 

 costal muscle and the greater pectoral, and end in the integument of the 

 breast, receiving the name of the anterior cutaneous nerves of the thorax. 



At the anterior part of the chest some of the muscular twigs cross the cartilages 

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



(a) The lateral cutaneous nerves of the thorax pierce the external intercostal 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 unusually 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 branches are continued forwards over the border of the great 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 posterior branches turn backwards to the integument over the scapula and the 

 latissimus dorsi muscle. The branch from the third nerve ramifies in the axilla, and 

 a few filaments reach the arm. 



The intercosto-humeral nerve, the lateral cutaneous branch of the second inter- 

 costal nerve, 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 in 

 the integument of the upper half of the arm, on the inner and posterior 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-lmmeral nerve, 

 and the extent of its distribution, are in the 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 supraclavicular 

 and the lateral cutaneous nerves; those from the third and fourth nerves are distri- 

 buted 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). 



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

 the external intercostal and external oblique muscles, in a line with the correspond- 

 ing 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 superficial 

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

 The posterior branches bend backwards over the latissimus dorsi muscle. 



(b) The anterior cutaneous nerves of the abdomen become subcutaneous near the 



