604 FUNCTIONS OF THE CEREBRO -SPIN AL NERVOUS SYSTEM. 



half of the Cord ; and, in like manner, all the longitudinal fibres belonging 

 to the anterior roots first enter the vesicular substance, and either terminate 

 in the gangliouic cells in the anterior horn or re-enter the anterior column, 

 or the anterior part of the lateral column, of the same or of the opposite 

 side. 



484. The observations of Mr. Clarke show clearly that some of the fibres 

 of the anterior roots never become longitudinal, and these, accordingly, have 

 no other ganglionic centre than the vesicular substance of the segment of the 

 Cord with which they come into immediate relation ; they also render it ex- 

 tremely probable, that many of the longitudinal fibres of both roots pass con- 

 tinuously upwards to the Encephalon, most of them after traversing the gray 

 nucleus, but some of those of the posterior roots without even entering the 

 vesicular substance, so that these cannot have their ganglionic centre in the 

 Cord at all. If the latter be among the fibres which pass up through the 

 Posterior Pyramids into the sensory tract of the Crura Cerebri, their true 

 ganglionic centres are the Thalami Optici. 



485. That such is the real arrangement, is very strongly indicated by the 

 analogous conformation of the gangliated cord of Articulated animals ; for 

 it may be stated with tolerable certainty, that some of the root-fibres of their 

 nerves pass along the purely fibrous tract of that cord (which is far more 

 readily separated from the vesicular, than it can be in Vertebrata), directly 

 to the cephalic ganglia, which they thus bring into direct communication 

 with all the nerve-trunks connected with the gangliated cord ; but that 

 others, also becoming longitudinal, and running along those portions of the 

 cord which intervene between and connect the ganglia of the different seg- 

 ments, pass into the nerve-trunks that emerge from ganglia at a distance of 

 one, two, three, or more segments above or below : whilst a large proportion 

 of the root-fibres have their ganglionic centres in the ganglia which they re- 

 spectively enter ; and, after coming into relation with its vesicular substance, 

 pass out again, either on the same or on the opposite side of the median 

 plane. 1 Now the purely fibrous tract of the ventral cord of the Articulata 

 terminates in the Cephalic ganglia, which are homologous, as already re- 

 marked ( 447, iv), not with the whole Encephalon of Vertebrata, but with 

 their "sensory ganglia" alone; and thus analogy would lead us to suppose, 

 that the fibrous strands of the Spinal Cord do not pass on continuously to the 

 Cerebrum, but really extend no further upwards than the Corpora Striata, 

 Thalami Optici, and the other ganglionic centres in connection with them 

 which lie along the floor of the cranial cavity. This view will be hereafter 

 shown (Sect. 3) to be in harmony with anatomical and physiological facts, 

 which indicate that the Cerebrum only receives its impulses to action through 

 the medium of the Sensory Ganglia, and that it reacts upon the muscular 

 apparatus only through the same channel. That some of the afferent fibres 

 of the spinal nerves should ascend continuously upwards to the ganglia of 

 tactile sense, in Man and other Vertebrata, as well as in Articulated animals, 

 would seem a legitimate deduction from the fact, that such continuity ob- 

 viously exists between the olfactive, visual, and auditory nerves, and their 

 respective, ganglionic centres, no intermediate apparatus of vesicular matter 

 being interposed in their course; and, as we have seen ($ 482), the existence 

 ol'sneli a continuity in regard to a part of the fibres of the posterior roots of 

 the nerves, is made extremely probable by the researches of Mr. J. L.Clarke. 

 A very remarkable confirmation, too, has been afforded to the doctrine of the 



1 SIT Prine. of Coinj). Pliys., \ 648. The important facts here referred to have 

 been rliirlly Militant intcd by' tho researches of Mr. Newport and M. Gunther. 



