Cervical 



12 Thoracic 



5 Lumbar 



5 Sacral 



FIG. 179. DIAGRAM OP 

 SPINAL NERVES. 



CHAPTER XX 

 THE SPINAL NERVES 



There are thirty-one pairs of spinal 

 nerves. They leave the spinal canal at 

 the intervertebral foramina in the differ- 

 ent regions and are named accordingly. 



Cervical 8 



Thoracic 12 



Lumbar 5 



Sacral 5 



Coccygeal. 



The first cervical, emerging above the atlas, 

 is called the suboccipital. 



The cauda equina. The spinal cord, being 

 17 inches long, reaches only to the second 

 lumbar vertebra, therefore the nerves emerg- 

 ing through the foramina below this level must 

 have lain in the canal for some distance before 

 leaving it, especially those which appear in 

 the lowest or pelvic region. If the canal be 

 opened at the back and the cord lifted out, 

 these long nerves are seen hanging from it in 

 a crowd, suggesting the appearance of a 

 horse's tail, the "cauda equina," which there- 

 fore is composed of the lumbar, sacral, and coc- 

 cygeal nerves while they are still in the neural 

 canal. The terminal filament extends down- 

 ward in their midst. 



All spinal nerves divide at once into 

 posterior and anterior divisions, both di- 

 visions containing motor and sensory 

 fibers (Fig. 181). 



The posterior divisions send nerves 

 to posterior regions of neck and trunk ; 

 the anterior divisions (communicate with 

 the sympathetic system, and then) send 

 nerves to anterior and lateral regions of 

 284 



