666 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



reduced to its minimum; and in the upper cervical region it is considerably 

 less than in the segments below. These and similar statements, however, have 

 been recently met by Prof. Kblliker, 1 who inclines to the first of the doctrines 

 stated in the preceding paragraph; his own researches having led him to a con- 

 clusion opposed to that of Volkmann, although he was at one time disposed to 

 coincide with it. He has assured himself that in Man the thickness of the 

 white columns augments from below upwards, and that the increase in the 

 diameter of the Cord at the ganglionic enlargements is due to the augmentation 

 of the gray matter only. Moreover, the diameter of the nerve-tubes in the 

 Cord, especially at its upper part, is so much smaller than the diameter of the 

 nerve-tubes of the Nerve-roots, that a large allowance must be made for this 

 difference in estimating the relative number of nerve-tubes in the fibrous 

 columns of the Cord and in the spinal Nerves; and he asserts, from actual 

 measurement, that it is by no means impossible for the fibrous strands of the 

 former to contain all the nerve-tubes which issue from them in the latter. He 

 has found himself unable, moreover, to detect any termination of nerve-fibres 

 in the vesicular substance of the spinal cord ; and hence he thinks it probable 

 that they all pass upwards to the brain. 



701. The researches of Prof. Kolliker have thus shown it to be quite possible 

 that many of the nerve-fibres (to say the least) do pass continuously between 

 the Encephalon and the nerve-roots; whilst there is an antecedent probability, 

 derived from the relation of these fibres to the vesicular substance of the Cord, 

 and from the attributes of each segment of the cord as an independent ganglionic 

 centre, that some of them terminate there. This probability becomes very strong 

 when the Spinal Cord is compared with the ventral column of the Articulata ; 

 for it may be stated, with certainty, that some of the root-fibres of the nerves 

 proceeding from the latter have their ganglionic centres in the vesicular matter 

 of the ganglia; whilst it is equally certain that some of the fibres pass along the 

 purely fibrous tract of the cord, directly to the cephalic ganglia, which they 

 thus connect with the roots of all the nerves. 2 But this fibrous tract terminates 

 in the Cephalic ganglia, which are homologous, as already remarked ( 674), 

 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 ex- 

 tend 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 har- 

 mony 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 pass 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 obviously exists between the olfactive, visual, and auditory 

 nerves, and their respective ganglionic centres, no intermediate apparatus of vesi- 

 cular matter being interposed in their course ; and there seems no reason why 

 the motor fibres which are instrumental in those movements that are dependent 

 upon antecedent or coexistent sensations, should not pass continuously from 

 these sensorial centres to the muscles which are called into action. If such 



1 " Mikroskopische Anatomie," Band ii. $ 116. 



2 See " Princ. of Phys., Gen. and Comp.," 768, Am. Ed. The important facts here re- 

 ferred to, have been chiefly substantiated by the researches of Mr. Newport ; a very impor- 

 tant addition to his statements, however, has been recently made by M. Gunther, who has 

 demonstrated the actual continuity between the nerve-fibres and the caudate vesicles, in 

 the ganglia of the ventral cord of the Leech. 



