STRUCTURE OF THE SPINAL CORD. 



297 



Origin of anterior 

 roots of nerves. 



From 11 to 11, the eight anterior roots of the cervical 

 nerves ; from 12 downward, the same roots of the dorsal 

 nerves : those of the lumbar and sacral are not shown in 

 the figure. As at 15, are shown the anterior branches of 

 the spinal nerves ; as at 16, their posterior branches ; at 

 17, spinal ganglia formed on the posterior roots ; 18, ante- 

 rior roots cut ; 19, anterior roots cut beyond the ganglion ; 

 20, dentated ligament, separating anterior from posterior 

 roots ; 21, insertion of this ligament on dura mater by its 

 dentated edge ; 22, insertion of same ligament on the pia 

 mater. 



Fig. 142 illustrates the origin of the posterior roots of 

 the spinal nerves. 1, tubercnla quadrigemina ; 2, trian- 

 gular band ; 3, 3, superior peduncles of the cerebellum ; 

 4, 4, middle peduncles of cerebellum ; 5, 5, inferior pedun- 

 cles of cerebellum ; 6, anterior wall of fourth ventricle ; 7, 

 glosso-pharyngeal ; 8, pneumogastric ; 9, spinal accessory ; 

 from 10 to 10, posterior roots of eight cervical pairs : the 

 dorsal, the lumbar, and the sacral below 11 are not shown 

 in the figure. From 14 downward, a dotted line arising 

 from the tearing away of the posterior roots ; 15, 15, an- 

 terior roots of spinal nerves, the dentated ligament being 

 visible through the removal of the posterior roots ; 16, spi- 

 nal ganglia, of which there are thirty pairs, the first pair 

 of nerves not being furnished with them ; 17, 17, anterior 

 branches of spinal nerves ; 18, 18, posterior branches; 

 19, 19, dentated ligament, placed between the posterior 

 and anterior roots ; 20, same ligament brought into view. 



Fig. 143 shows a portion of the spinal cord mgm 143- 

 surrounded by its envelopes, and seen in pro- 

 file, so as to display at once the origin of the 

 anterior and posterior roots. 1,1, posterior 

 roots of spinal nerves and their ganglia ; 2, 2, anterior roots 

 of the same nerves anastomosing with the anterior portions 

 of these ganglia; 3, 4, anterior and posterior roots cut; 

 5, dentated ligament ; 6, dura mater, preserved to show the 

 sheaths which it forms around these ganglia and the branches 

 of the spinal nerves ; 7, vertical section of the sheath of the 

 anterior and posterior roots, to show the little lamella which 

 separates the one root from the other; 8, 8, interior face. of 

 the dura mater, which is drawn aside to show the smooth 

 aspect which it possesses, owing to the parietal layer of the rior rootSt 

 arachnoid which covers it. 



J.gin of posterior 

 roots of nerves. 



