THE DISSECTION OF THE BACK 



81 



and finally ends, at the level of the second sacral vertebra, 

 by blending with the filum terminate, a fibrous thread which 

 is prolonged downwards through the sacral canal from the 

 extremity of the medulla spinalis (O.T. spinal cord). 



The cylindrical tube of spinal dura mater does not 

 lie free within the vertebral canal, but its attachments 

 do not in any way interfere with the free movement of 



Dura mater 

 ^-Arachnoid 

 Ligamentum denticulatum 



Arachnoid 



Posterior nerve-root 

 Spinal ganglion 



Anterior ramus 

 of nerve 



Posterior ramus 

 of nerve 



Dura mater 



Anterior nerve-root 

 (cut) 



Posterior nerve-root 



Anterior nerve-root 

 (cut) 



Ligamentum 

 denticulatum 



Pia mater 



Anterior nerve-root 



FIG. 2i. Membranes of the. Medulla Spinalis (O.T. Spinal Cord), and the 

 mode of origin of the Spinal Nerves. 



the vertebral column. Above, the dura mater is firmly 

 attached around the margin of the foramen magnum, and 

 to the bodies of the' second and third cervical vertebrae ; 

 below, the filum terminale, on which the dura mater termin- 

 ates, can be traced as far as the dorsum of the coccyx, where 

 it is lost by blending with the periosteum. On each side, the 

 spinal nerve-roots, as they pierce the dura mater, carry with 

 them, into the intervertebral foramina, tubular sheaths of the 

 membrane, which are attached to the margins of the foramina ; 

 whilst, anteriorly, loose fibrous prolongations more numerous 

 VOL. in 6 



