THE LAST DORSAL NERVE. 311 



nerves on the thorax, and divide in the same manner into anterior and posterior 

 branches. 



The anterior IrancJws are the larger. They supply the digitations of the external 

 oblique muscle, and are then directed inwards, the lower nerves also inclining 

 downwards, 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. 



The anterior cutaneous nerves of the abdomen are uncertain in number 

 and position. There are generally two or three twigs from each nerve, and some of 

 them perforate the rectus near its outer border, but the greater number issue near 

 the linea alba. The branches of the seventh nerve emerge near the lower end of the 

 ensiform process, and those of the tenth usually supply the skin about the 

 umbilicus. 



LAST DOBSAL NERVE. 



The anterior primary division of the last dorsal nerve is directed outwards in 

 company with the abdominal branch of the first lumbar artery along the lower border 

 of the twelfth rib. It passes beneath the external arched ligament of the diaphragm, 

 across the front of the quadratus lumborum, and at the outer border of the latter 

 muscle it perforates the posterior aponeurosis of the transversalis (middle layer of 

 the lumbar fascia), to follow a course similar to that of the lower intercostal nerves 

 in the abdominal wall. It is usually connected near its origin with the first 

 lumbar nerve by means of a small cord, which descends on or through the substance 

 of the quadratus lumborum muscle. It supplies branches to the quadratus 

 lumborum (frequently), internal oblique, transversalis, rectus, and pyramidalis 

 muscles, as well as lateral and anterior cutaneous branches ; and it sometimes com- 

 municates in the abdominal wall with the ilio-hypogastric nerve. Its anterior 

 cutaneous twigs are distributed below a point midway between the umbilicus and 

 pubis. 



The lateral cutaneous branch of the last dorsal nerve is usually of considerable 

 size. It pierces the internal oblique muscle, gives a branch to the lowest slip of the 

 external oblique, and then emerging through the latter muscle a variable distance 

 (from one to three inches) above the iliac crest, is directed downwards to the 

 integument of the fore part of the gluteal region, some filaments reaching as far as 

 the great trochanter. 



Varieties. In some cases the lateral cutaneous branch of the last dorsal nerve is small, 

 and is distributed entirely to the skin above the iliac crest, its place over the hip being taken 

 by the iliac branch of the ilio-hypogastric nerve. Complete absence of this branch was 

 observed by M. Griffin four times in fifty cases (" Some Varieties of the Last Dorsal and First 

 Lumbar Nerves," Journ. Anat., xxvi, 1891). 



LUMBAR NEEVES. 



The anterior divisions of the lumbar nerves increase in size from the first to the 

 fifth. The upper three and the greater part of the fourth enter the lumbar plexus ; 

 the smaller part of the fourth and the fifth pass down to the sacral plexus. On 

 leaving the inter vertebral foramina, the nerves are connected by filaments with the 

 cord of the sympathetic, these filaments being longer than those connected with 

 other spinal nerves, in consequence of the position of the lumbar sympathetic 

 ganglia on the fore part of the bodies of the vertebrae. In the same situation 

 small twigs are furnished to the quadratus lumborum muscle from the first and, 

 sometimes, the second nerve, and to the psoas from the second and third nerves. 



