310 THE SPINAL NERVES. 



The anterior branches are continued forwards over the border of the great 

 pectoral muscle. In the female their terminal ramifications supply the skin over the 

 mamma, and some filaments enter the substance of the gland. From the lowest two 

 nerves twigs are supplied to the upper 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 often reach the arm. 



The intercosto-humeral nerve (n. mtercosto-brachialis), the lateral cutaneous 

 branch of the second intercostal 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 (p. 296). 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-humeral nerve, and the extent of its distribution, are in 

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

 especially the nerve of Wrisberg. 



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. One or two of the upper branches may be connected with 

 the supraclavicular nerves. In the female, those from the second, third, and fourth 

 nerves are distributed over the mammary gland. 



Varieties. At the hinder part or side of the chest some of the adjacent intercostal 

 nerves are occasionally connected by filaments which cross the inner surfaces of the ribs, 

 passing from one intercostal space to join the nerve in the interval next below. A twig' from 

 the second intercostal nerve to the pectoralis major has been described by Swan and M. Flesch ; 

 one to the pectoralis minor by Brooks. 



LOWER OR ABDOMINAL INTERCOSTAL NERVES. 



The lower intercostal nerves in the first part of their course have relations like 

 those of the upper nerves already described. Lying between the external and 

 internal intercostal muscles, they give off the lateral cutaneous branches, and at the 

 fore part of the intercostal spaces they penetrate the internal intercostal muscles. 

 They then pass between the slips of origin of the diaphragm, the seventh, eighth, 

 and ninth nerves each crossing behind the cartilage of the rib below, and enter the 

 abdominal wall. Here they are continued between the internal oblique and 

 transversalis muscles as far as the outer edge of the rectus, diverging from one 

 another as they pass inwards, in consequence of the increasing obliquity of the 

 lower nerves. Finally, perforating the posterior layer of the sheath of the rectus, 

 they turn forwards through the substance of that muscle and the anterior layer of its 

 sheath to end in small cutaneous branches (anterior cutaneous nerves) . While between 

 the abdominal muscles the lower three or four nerves are united by loops of com- 

 munication, and sometimes form a small plexus. 



BRANCHES. Muscular branches are given to the levatores costarum, to the 

 serratus posticus inferior (from the ninth, tenth, and eleventh nerves), to the 

 subsostal and intercostal muscles, and to the abdominal muscles with which 

 the nerves are in contact. Filaments are also described as passing from these nerves 

 to the costal portion of the diaphragm (Baur, Swan, Luschka). 



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 



