IQ22 THE NERVE SYSTEM 



pierce the aponeurosis of the Latissimus dorsi muscle and descend over the back 

 part of the crest of the ilium, to be distributed to the integument of the gluteal 

 region, some of the filaments passing as far as the trochanter major (Fig. 771). 



The posterior division of the fifth lumbar nerve usually sends a branch which 

 forms a loop with the posterior division of the first sacral nerve. 



The Posterior Divisions of the Sacral Nerves (rami posteriores) (Fig. 772). 

 The posterior divisions of the sacral nerves are small, diminish in size from above 

 downward, and emerge, except the last, from the sacral canal by the posterior 

 sacral foramina. The upper three are covered at their exit from the sacral canal 

 by the Multifidus spinae muscle, and divide into internal or medial and external 

 or lateral branches. 



The internal branches (rami mediales) are small, and supply the Multifidus 

 spinae muscle. 



The external branches (rami laterales) join with one another, and with the 

 last lumbar and fourth sacral nerves, in the form of loops on the posterior surface 

 of the sacrum, constituting the posterior sacral plexus. From these loops branches 

 pass to the outer surface of the great sacrosciatic ligament, where they form 

 a second series of loops beneath the Gluteus maximus muscle. Cutaneous 

 branches from this second series of loops, usually two or three in number, pierce 

 the Gluteus maximus muscle along the line drawn from the posterior superior 

 spine of the ilium to the tip of the coccyx. They supply the integument over the 

 posterior part of the gluteal region. 



The posterior divisions of the lower two sacral nerves are small and lie below 

 the Multifidus spinae muscle. They do not divide into internal and external 

 branches, but join with each other, and with the posterior division of the coccygeal 

 nerve to form the posterior sacrococcygeal nerve, which passes through the sacro- 

 sciatic ligament, and forms loops on the back of the sacrum, filaments from which 

 supply the integument over the coccyx. 



The Posterior Division of the Coccygeal Nerve. The coccygeal nerve divides 

 into its anterior and posterior divisions in the vertebral canal. The posterior 

 division is the smaller, and it does not divide into internal and external branches, 

 but receives, as already stated, a communicating branch from the last sacral, 

 and is lost in the integument over the dorsum of the coccyx. 



Anterior or Ventral Primary Divisions of the Spinal Nerves. The anterior 

 primary divisions of the spinal nerves (rami anteriores) supply the antero-lateral 

 parts of the trunks and the limbs; they are, for the most part, larger than the 

 posterior divisions. In the thoracic region they run independently of one another, 

 but in the cervical, lumbar, and sacral regions they unite near their origins to 

 form plexuses. 



The Anterior or Ventral Divisions of the Cervical Nerves (rami anteriores). 

 The anterior primary divisions of the cervical nerves, with the exception of the first, 

 pass laterad between the anterior and posterior Intertransverse muscles, lying 

 on the grooved upper surfaces of the transverse processes, and emerge between 

 the muscles attached to the anterior and posterior tubercles of these processes. 

 The anterior primary division of the first or suboccipital nerve issues from the 

 vertebral canal above the posterior arch of the atlas and runs forward around the 

 lateral aspect of its superior articular process, internal to the vertebral artery. 

 In most cases it descends internal to and in front of the Rectus lateralis, but in 

 some cases it pierces the muscle. 



The anterior primary divisions of the upper four cervical nerves unite to form 

 the cervical plexus, and each receives a gray ramus communicans from the superior 

 cervical ganglion of the sympathetic cord. Those of the lower four cervical, 

 together with the greater part of the first thoracic, form the brachial plexus. They 



