362 THE SOLIDS. 



pendent upon a difference of structure. The great sympa- 

 thetic cord itself, and the organic nerves connected with it, 

 arc composed of two distinct descriptions of fibre ; first, 

 of the ordinary tubular fibre, which, however, is of small 

 diameter, and therefore readily becomes varicose, and second, 

 of nucleated filaments, in every appreciable respect resem- 

 bling those of unstriped muscular fibre. Henle has called 

 these fibres "gelatinous nerve fibres." 



The relative proportions existing between these two kinds 

 of fibre differs in different nerves: thus in some cases the 

 gelatinous fibres are by far the most numerous ; in others, the 

 tubular fibres preponderate. The gelatinons or grey fila- 

 ments arc best seen in what are called the roots of the 

 sympathetic ; that is to say, in the branches which accom- 

 panying the carotid artery, proceed from the superior cervical 

 ganglion to the fifth and sixth pair of cerebral nerves, and 

 in those which descend from the same ganglion and follow the 

 course of the carotid. In these the proportion of tubular 

 fibres is but small, as one to six ; and they are also isolated 

 from, each other, each being surrounded with a number of 

 gelatinous fibres. This disposition of the nucleated fibres 

 has led Valentin to consider that they form a sheath around 

 the tubular fibres, each grey nerve, according to that ob- 

 server, being composed of a number of fascicles or bundles. 

 Henle, however, objects to this view, considering that the 

 fibres are too large for a sheath, and remarking that the grey 

 nerves do not separate into such bundles, but divide much 

 more readily in such a way as that the tubular fibre is found 

 at the border of the bundle. Henle, therefore, considers it 

 to be more natural to regard the grey nerves as forming solid 

 threads, composed of nucleated filaments between which the 

 tubular fibres run. 



The tubular fibres are more numerous than in the roots of 

 the great sympathetic in the majority of the visceral nerves, 

 in the branches which proceed from the cardiac and hypo- 

 gastric plexuses, &c. ; in these the tubular fibres may be seen 

 enclosed within the grey filaments, forming many bundles. 

 Their number becomes still more considerable in the great 



