THE NERVE SYSTEM 



the inner and back part of the arm (Figs. 762 and 763), communicating with the 

 internal cutaneous branch (n. cutaneus antebrachii medialis) of the musculospiral 

 nerve. The size of this nerve is in inverse proportion to the size of the other 

 cutaneous nerves, especially the nerve of Wrisberg. A second intercostohumeral 

 nerve is frequently given off from the third intercostal. It supplies filaments to 

 the armpit and inner side of the arm. It may or may not send a branch to the 

 intercostohumeral. 



The Anterior Divisions of the Seventh, Eighth, Ninth, Tenth, and Eleventh Thoracic 

 Nerves are continued anteriorly from the intercostal spaces into the abdominal 

 wall; hence these nerves are named thoracoabdominal intercostal nerves. They 

 have the same arrangement as the upper ones as far as the anterior extremities 

 of the intercostal spaces, where they pass behind the costal cartilages, and between 

 the Internal oblique and Transversalis muscles, to the sheath of the Rectus, which 

 they perforate. They supply the Rectus muscle, and terminate in branches 

 which become subcutaneous near the linea alba. These branches are named 

 the anterior or ventral cutaneous nerves of the abdomen. They are directed outward 

 as far as the lateral cutaneous nerves, supplying the integument of the front of 

 the belly. The lower intercostal nerves supply the Intercostals, Serratus posticus 

 inferior, and Abdominal muscles, and, about the middle of their course, give off 

 lateral cutaneous branches which pierce the External intercostal and External 

 oblique muscles, in the same line as the lateral cutaneous nerves of the thorax, 

 and divide into anterior and posterior branches, which are distributed to the integu- 

 ment of the abdomen and back; the ventral branches supply the digitations of 

 the External oblique and extend downward and forward nearly as far as the margin 

 of the Rectus muscle; the posterior branches pass backward to supply the skin 

 over the Latissimus dorsi. 



The Anterior Division of the Last Thoracic Nerve is larger than that of the other 

 thoracic nerves; it runs along the lower border of the last rib, and passes under 

 the external arcuate ligament of the Diaphragm. It then runs in front of the 

 Quadratus lumborum muscle, perforates the Transversalis muscle, and passes 

 between it and the Internal oblique muscle, to be distributed in the same manner 

 as the lower intercostal nerves. It communicates with the iliohypogastric branch 

 of the lumbar plexus, and is frequently connected with the first lumbar nerve 

 by a slender branch, the thoracicolumbar nerve, which descends in the substance 

 of the Quadratus lumborum muscle. It gives a branch to the Pyramidalis muscle. 



The lateral cutaneous branch of the last thoracic (ramus cutaneus lateralis [ab- 

 dominalis] intercostalis XII) is remarkable for its large size. It does not divide 

 into an anterior and a posterior branch, like the other lateral cutaneous branches 

 of the intercostal nerves, but perforates the Internal and External oblique muscles, 

 passes over the crest of the ilium in front of the iliac branch of the iliohypogastric, 

 and is distributed to the integument of the front part of the gluteal region, some 

 of its filaments extending as low down as the trochanter major. 



Applied Anatomy. The lower seven intercostal nerves and the iliohypogastric from the 

 first lumbar nerve supply the skin of the abdominal wall. They run downward and inward 

 fairly equidistant from each other. The sixth and seventh supply the skin over the "pit of the 

 stomach;" the eighth corresponds to about the position of the middle linea transversa; the tenth 

 to the umbilicus; and the iliohypogastric supplies the skin over the pubes and external abdominal 

 ring. There are several points of surgical significance about the distribution of these nerves, 

 and it is important to remember their origin and course, for in many diseases affecting the nerve 

 trunks at or near their origin the pain is referred to their 'peripheral origins. Thus, in 

 Putt's disease of the .spine children will often be brought to the surgeon suffering from ain 

 m_t]ie_bellv. This is due to the fact that the nerves are irritated at the seat of disease as they 

 issue from the vertebral canal. When the irritation is confined to a single pair of nerves, the sen- 

 sation complained of is often a feeling of constriction, as if a cord were tied around the abdomen; 

 and in these cases the situation of the sense of constriction may serve to localize the disease in 



