INTERCOSTAL XERVES— THORACIC XERVE SOI 



noous branch of the second intercostal nerve is called the intercosto-humeral 

 nerve. It passes outwards across the axillary space, crosses the tendon of the 

 latissimus dorsi and the internal cutaneous branch of the musculo-spiral nen-e to 

 reach the ami. It is distril;»uted to the integument of the inner and posterior part 

 of the ann in its U{)per two-thirds. Within the axilla it connnunicates with the 

 lesser internal cutaneous ner%'e of the brachial plexus, and with the lateral cutane- 

 ous bnuicli of the third intercostal. The lateral cutaneous branch of the third 

 intercostal divides intt» a small anterior and a larLa- ]t<'>ttri(>r brancli. The ante- 

 rior branch ends near the margin of the great {>ectoral muscle. The posterior 

 branch communicates with the intercosto-humeral nerve, and then turns round the 

 posterior fold of the axilla, and, after giving a twig to the integument of the arm, 

 ends in the skin ctivering the dorsum of the scapula. 



The anterior cutaneous nerves of the thorax are the terminal branches of 

 the upper intercostal nen'es. Thev i>ierce the pect oralis major in company with 

 the perforating branches of the internal mammary artery. On reaching the surface 

 of the muscle, they give off minute twigs, Avhich supply the skin over the steniiim, 

 and then end in slender branches which are directed outwards to supply the skin 

 covering the greater part of the pectoralis major. Some twigs from the third, 

 fourth, tifth, and sixth ner\-es are distributed to tlie mammary gland. 



C. Lower intercostal nerves. — The seventh, eighth, ninth, tenth, and 

 eleventh intercostal nerves, in the part of their course which lies between the ribs, 

 present the same relations as the upper intercostal nerves. Leaving the intercos- 

 tal spaces they pass behind, or in the last two spaces between the costal cartilages, 

 and then forwards between the internal oblique and transversalis muscles,, where 

 they anastomose together, in a plexiform manner. Piercing the posterior lamella 

 of the internal oblicjue aponeurosis, they enter the sheath of the rectus abdominis; 

 they supjdy the rectus muscle, pass through it, pierce the anterior part of its sheath 

 ami tenninate as the anterior cutaneous nerves in the skin of the abdomen. 



Branches. — The lower intercostal ner\-es supply the external and internal 

 intercostal muscles, the levatores costarum, the serratus posticus inferior, the inter- 

 nal oblique, the transversalis, the rectus, and from one or more of them twigs are 

 given to the costal fibres of the diaphragm. They also give off lateral cutaneous 

 branches, by which the external oblique is supplied. 



The lateral cutaneous nerves of the abdomen are the continuation of the 

 series of tlie lateral cutaneous nerves of the tliorax. They divide into anterior and 

 posterior branches, which pierce the external oblii|ue. The anterior branches 

 are directed fc^rwards and somcAvhat downwards, and supply the integument e<ner- 

 ing the anterior abdominal wall as far as the outer margin of the rectus. Each 

 nerve gives ofl" a muscular twig, which pierces the adjacent diiritation of the exter- 

 nal obli(jue muscle on its superficial surface. The posterior branches pass back- 

 wards around the margin of the latissimus dorsi. and end in the skin of the outer 

 part of the back. 



The anterior cutaneous nerves of the abdomen are the terminal branches 

 of the lower intercostal nerves, and pierce tlu- anterior part of the sheath of the 

 rectus to supply the skin covering that muscle. These nerves are of small size, and 

 sometimes divide before their emergence, so as to fonu a double series. 



D. Last thoracic nerve. — This nerve gives off a communicating twig to the 

 first lumbar nerve, and tlien passes lieneath the external arcuate ligament, and runs 

 outwards below the twelfth ril) across the front of the quadratus lumborum, accom- 

 panied by the first lumbar artery. It pierces the posterior aponeurosis of the trans- 

 versalis, and follows the curve of the abdominal wall between the transversalis and 

 internal ol)lique muscles. In the remainder of its course it resembles a lower 

 intercostal nerve. After piercing the rectus, however, it supplies the pyramidalis 

 ((Jriffin). Its lateral cutaneous liranch remains undivided, and represents the 

 anterior division of an ordinary lateral cutaneous branch. On account of its dis- 

 tribution, it is named the iliac branch. The iliac branch pierces the external 

 obli(|ue about three inches above the iliac crest, and is ilireeted downwards, acro.cs 

 the crest, a short distance behind the anterior superior .spine. It ends in the 

 integument covering the anterior part of the gluteal region. 

 51 



