THE SPINAL NERVES 1021 



joined beneath the Complexus by communicating loops to form the posterior 

 cervical plexus (Cruveilhier). 



The posterior divisions of the lower five cervical nerves pass dorsad, and divide, 

 behind the Intertransversales muscles, into internal or medial and external or 

 lateral branches. 



The internal branches, the larger, are distributed differently in the upper and 

 lower part of the neck. Those derived from the fourth and fifth nerves pass 

 between the Complexus and Semispinalis muscles, and, having reached the spinous 

 processes, perforate the aponeurosis of the Splenius and Trapezius, and are con- 

 tinued outward to the integument over the Trapezius, while those derived from 

 the three lowest cervical nerves are the smallest, and are placed beneath the Semi- 

 spinalis colli, which they supply, and then pass into the Interspinalis, Multifidus 

 spinae, and Complexus, and send twigs through this latter muscle to supply the 

 integument near the spinous processes. 



The external branches supply the muscles at the side of the neck viz., the 

 Cervicalis ascendens, Transversalis colli, and Trachelomastoid. 



The Posterior Divisions of the Thoracic Nerves (rami posteriores). The 

 posterior divisions of the thoracic nerves are smaller than the anterior, pass 

 dorsad between the transverse processes, and divide into internal or medial and 

 external or lateral branches. 



The internal or medial branches of the posterior divisions of the six upper thoracic 

 nerves pass inward between the Semispinalis dorsi and Multifidus spinae muscles, 

 which they supply, and then, piercing the origins of the Rhomboidei and Trapezius 

 muscles, become cutaneous by the side of the spinous processes and ramify in 

 the integument. The medial branches of the six lower thoracic nerves are dis- 

 tributed to the Multifidus spinae, without giving off any cutaneous filaments. 



The external or lateral branches increase in size from above downward. They 

 pass through the Longissimus dorsi muscle to the cellular interval between it and 

 the Iliocostalis muscle, and supply those muscles, as well as their continuations 

 upward to the head, and also the Leva tores costarum muscles; the five or six 

 lower nerves also give off cutaneous filaments, which pierce the Serratus posticus 

 inferior and Latissimus dorsi muscles in a line with the angles of the ribs, and 

 then ramify in the integument. 



The cutaneous branches of the posterior primary divisions of the thoracic nerves 

 are twelve in number. From each ramus medialis of the upper six nerves comes 

 a ramus cutaneiLs medialis, and from each ramus lateralis of the lower six nerves 

 comes a ramus cutaneus lateralis. The six upper cutaneous nerves are derived 

 from the internal branches of the posterior divisions of the thoracic nerves. They 

 pierce the origins of the Rhomboidei and Trapezius muscles, and become cutaneous 

 by the side of the spinous processes, and then ramify in the integument. They 

 are frequently furnished with gangliform enlargements. The six lower cuta- 

 neous nerves are derived from the external branches of the posterior divisions 

 of the thoracic nerves. They pierce the Serratus- posticus inferior and Latissi- 

 mus dorsi muscles in a line with the angles of the ribs, and then ramify in the 

 integument. 



The Posterior Divisions of the Lumbar Nerves (rami posteriores*). The 

 posterior divisions of the lumbar nerves diminish in size from above downward; 

 they pass postero-laterad between the transverse processes, and divide into internal 

 or medial and external or lateral branches. 



The internal branches (rami mediates), the smaller, pass inward close to the 

 articular processes of the vertebrae, and supply the Multifidus spinae and Inter- 

 spinales muscles. 



The external branches (rami .later ales) supply the Erector spinae and Inter- 

 transverse muscles. The three upper branches give off cutaneous nerves wnich 



