THE DISSECTION OF THE BACK 



191 



the atlas, and the second cervical nerve by passing over the 

 vertebral arch of the epistropheus (O.T. axis). The fifth 

 sacral and the coccygeal nerve leave the sacral canal through 

 its lower aperture (Fig. 78). 



Dissection. The nerve-roots of one or two spinal nerves in each 

 region should be followed into the corresponding intervertebral foramina. 



Filum terminale 

 Cauda equina 



Dura mater 



Filum 

 terminale 

 Fifth sacral nerve 



Coccygeal nerve 



FIG. 78. The Sacral Nerve-roots (lower part of Cauda Equina) and the 

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

 Sacral Canal is removed. 



This can be easily done by snipping away the articular processes with the 

 bone-forceps. The position of the ganglion" on the posterior root, the 

 connections of the sheath of dura mater, the union of the two roots to form 

 the spinal nerve-trunk, and the division of the latter into the anterior 

 and posterior branches can thus be studied. An attempt should also 

 be made at the same time to discover the minute ratnus meningeiis. 

 This is a fine twig which is formed by the union of a small filament from 

 the spinal nerve-trunk with a minute branch from the sympathetic trunk. 



