166 



ANATOMY OF VERTEBRATES. 



135 



fissure., and between the bundles passes a delicate fold of the arach- 

 noid, which is attached by an angular process, d } to the dura-mater 

 at the interval, usually, of each nerve (p. 7 8). 

 The anterior or ventral and the posterior or 

 dorsal bundles converge, separately per- 

 forate the dura-mater, and unite, at the in- 

 tervertebral foramen, into a single ( nerve.' 

 In the Elephant the posterior roots come 

 off abruptly in a few, large, and distinct 

 bundles : the anterior roots emerge from 

 a longer extent of their furrow, are nume- 

 rous and small, and form several bundles 

 before passing through the dura-mater. 

 The same characters of the anterior and 

 posterior origins are seen in Cetacea, in 

 which the two roots preserve their distinct 

 course before uniting, after perforating the 

 dura-mater, longer than in other Mam- 

 mals. In the human 

 subject, especially 

 at the cervical part 

 of the myelon, the 

 anterior root, fig. 

 136, A, is the small- 

 est; its finer fila- 

 ments form more 

 delicate fasciculi, 

 affffregatinff into 

 two, before uniting, 

 as a flat band, with 

 the posterior root. 

 Of this the fila- 

 ments, p, are larger, 

 and blend with the 

 cell-substance of a 

 ganglion, G, before 

 uniting with the 

 anterior root to form 



— d 



Portion of myelon, with roots of 



nerves of one side. Human, 



natural size. 



Roots of myeloual nerve, magn. 



the nerve-trunk, c. 

 The capital experiment which has immortalised the name of 

 Charles Bell was suggested by the above anatomical fact, and 

 I quote his original account of it from the extremely rare little 

 tract, which he printed for private distribution in 181 1. 1 



1 LXIV. 



