502 NERVOUS SYSTEM. 



The anterior fasciculus of the first, as mentioned, forms the 

 lower part of the axillary plexus by joining itself to the se- 

 venth cervical. It sends out, however, a subcostal branch 

 which goes along, the inferior face of the first rib, supplying 

 the intercostal muscles and having the general distribution al- 

 luded to. 



The Second Subcostal Branch, besides the common distribu- 

 tion, detaches a fasciculus, which, penetrating between the ribs, 

 gets into the axilla, and is augmented by a branch from the 

 internal cutaneous nerve of the upper extremity. It then de- 

 scends along the internal posterior face of the arm to the elbow, 

 and in this course detaches several fine filaments to the integu- 

 ments. 



The Third Subcostal Branch in like manner detaches an 

 axillary fasciculus which goes to the inferior part of the arm- 

 pit, to the integuments of which, and to those on the internal 

 face of the arm, it is distributed. It does not descend quite so 

 low as the preceding. These two nerves are called Intercosto- 

 Humeral, and from their origin and course, are supposed to 

 account for the numbness of the arm, in cases of angina pec- 

 tori s. 



The Fourth, Fifth, Sixth, and Seventh Subcostal Branches 

 of the Dorsal or Thoracic Nerves, about the middle of the ribs 

 to which they respectively belong, are all divided into two 

 branches. One of them, which is properly speaking the in- 

 tercostal, continues in the intercostal space, giving filaments to 

 its muscles and to the triangularis sterni; it then emerges near 

 the sternum to terminate upon the great pectoral muscle, the 

 mamma, and the integuments of the front of the thorax. The 

 other branch is the external pectoral : it extricates itself earlier 

 from the intercostal space, and is distributed upon the muscles 

 and the integuments on the side of the thorax. 



The remaining subcostal branches, to the eleventh inclu- 

 sively, have very much the same principle of distribution. 

 Their intercostal fasciculi, having reached the anterior ends 

 of the intercostal spaces, pass on to the abdominal parietes, be- 

 tween the transversalis muscle and the internal oblique, to both 

 of which they give, filaments. They reach the external margin 

 of the rectus abdominis muscle, and then divide into filaments, 

 some of which go to this muscle, others pierce the fore part of 



