492 



THE SriNAL CORD. 



The terminal filament (filum terminale, central ligament) (fig, 

 oiG,b,h.) descends in the middle line amongst the nerves composing the 

 Cauda ecpiina, and, becoming blended -with the lower end of the sheath 

 opposite to the first or second sacral vertebra, passes on to be fixed 

 to the lower end of the sacral canal, or to the base of the coccyx. 



Fig. oio. 



Fig. 3io. — Posterior View op the IMedulla Oblongata and of the Spinal Cokd 

 WITH ITS CovERiNOs AND THE RooTS OF THE Nerves ^from Sappey). 4 

 The theca or dura-matral slieatli lias been opened by a median incision along the whole 

 length, and is stretched out to each side. On the left side, in the upper and middle parts 

 {A and B), the posterior roots of the nerves have been removed so as to expose the liga- 

 mentuni denticulatuni ; and along the right side the roots are shown passing out through 

 the dura mater. The roman numbers indicate the different nerves in the cervical, dorsal, 

 lumbar, and sacral regions ; 9, several of the pointed processes of the ligamentum deu- 

 ticulatum ; 10, oi-igin of several posterior roots ; 11, posterior median fissure ; 12, 

 ganglia of the spinal nerves ; 1.3, part of the anterior roots seen on the left side ; 14, 

 the united nerve ; 15, tapering lower end of the spinal cord ; It.!, filum terminale ; 17, 

 Cauda equina. 



Internally, it is a prolongation for about half its length of some of 

 the nervous elements of the cord : externally, it consists of a tube 

 of the pia mater or innermost membrane, which, being attached at its 

 lower end to the dura mater and vertebral canal, keeps pace with the 

 latter in its growth, whilst the cord relatively shortens. It is distin- 

 guished by its silvery hue from the nerves amid which it lies. Small 

 blood-vessels may sometimes be seen upon it. 



Fissures. — When removed from the vertebral canal, and divested 



