THE LUMBAR NERVES 365 



sternum, pierce the serratus magnus and external intercostals, 

 and each divides into two branches, anterior and posterior. 



The anterior runs to the skin over upper part of the external 

 oblique, mamma, and skin; the posterior, to the skin over the 

 scapula and latissimus dorsi. 



The lateral cutaneous of the second dorsal crosses to the 

 arm, joins the nerve of Wrisberg, pierces the fascia, and supplies 

 the skin of the upper half of the inner and back part of the 

 upper arm, joining the cutaneous branch of the musculospiral 

 nerve. This nerve is generally called the intercostohumeraL 

 It has no anterior division. 



The LOWER six, or abdominal intercostals, run from the 

 intercostal spaces behind the cartilages, between the internal 

 oblique and transversalis, to the rectus, which they enter. 

 They supply the intercostals, serratus posticus inferior, abdom- 

 inal muscles, and end in the skin, as the anterior cutaneous 

 nerves of the abdomen. 



The lateral cutaneous branches have a similar distribution 

 to those in the chest. 



The LAST DORSAL nerve is altogether abdominal. It crosses 

 the quadratus lumborum and runs into the abdominal wall 

 like the lower intercostals. It communicates with the ilio- 

 hypogastric and with the first lumbar nerve (dorsolumbar) . 

 Its lateral cutaneous branch supplies the skin of the forepart 

 of the gluteal region as low as the great trochanter. 



Each dorsal nerve is joined by short communicating branches 

 from the sympathetic. 



The Lumbar Nerves 



The Posterior Division. In the lumbar region the internal 

 branches end in the multifidus. The external supply the inter- 

 transverse muscles and erector spinse, and the upper three 

 a portion of the skin over the gluteal region. 



The Anterior Divisions of the Lumbar Nerves. The first unites 

 with a branch from the last dorsal, the dorsolumbar nerve, 

 and then proceeds, together with the second, third, and fourth, 

 to form the lumbar plexus. The fifth joins the sacral plexus. 

 They are joined by the sympathetic filaments, and furnish 

 branches to the psoas and quadratus muscles. 



