THE DISSECTION OF THE BACK 



89 



the posterior arch of the first and the vertebral arch of the 

 second cervical vertebrae, respectively ; the ganglia of the 

 sacral nerves are placed within the sacral canal, but out- 

 side the tube of dura mater. The ganglion on the posterior 

 root of the coccygeal nerve is inside the tube of dura mater. 



Filum terminals 



Filum 



.nale 

 Fifth sacral nerve 



Coccygeal nerve 



FIG. 25. The Sacral Nerve-roots (lower part of Cauda Equina) and the 

 Membranes in relation to them. (After Testut. ) The posterior wall of 

 Sacral Canal has been removed. 



Spinal Nerve -Trunks.- The trunks of the spinal nerves 

 are formed by the union of the anterior and posterior nerve- 

 roots immediately beyond the spinal ganglia. The union 

 takes place in the case of the coccygeal and sacral nerves 

 in the sacral canal ; in the lumbar, thoracic, and lower six 

 cervical nerves, in the intervertebral foramina ; and in the 

 case of the first two cervical nerves, on the arches of the 

 atlas and epistropheus respectively. 



