THE SPINAL CORD. 665 



them may be transmitted to many others, and may excite reflex movements 

 through them. Among those who hold this view, however, there is a very con- 

 siderable difference of opinion with regard to the real centre of the Encephalic 

 fibres; some maintaining that they pass through the Corpora Striata, Thalami 

 Optici, and other Sensory Ganglia, to the peripheral vesicular matter of the 

 Cerebrum; whilst others hold that the real termination of all of them is in the 

 Sensory Ganglia, and that the Cerebrum has therefore no connection with them, 

 otherwise than through the intermediation of those bodies. Although this 

 question may be considered as rather related to the structure and functions of 

 the Encephalic centres, than to that of the Spinal Cord, yet it has such a bear- 

 ing upon the function assigned to the longitudinal fibres of the Cord that it 

 must be taken into account in the present discussion. 



700. The principal argument for the doctrine (which seems to have origi- 

 nated with the anatomical researches of Stilling and Wallach, 1 and to have been 

 first put forth on a physiological basis by Messrs. Todd and Bowman 3 ) that the 

 Spinal Cord is the real centre of all the nerve-fibres connected with it, arises 

 from the asserted difficulty of supposing that its longitudinal columns can trans- 

 mit any considerable number of nerve-fibres from the Encephalon to the Spinal 

 nerve-roots. Thus it is urged by Dr. Todd, that it is highly improbable that 

 the only channel by which the Will can influence the spinal nerves should be 

 (as generally admitted) that afforded by the Anterior Pyramids; since the 

 whole bulk of these pyramids on both sides, taken together, scarcely equals that 

 of one of the anterior portions of the antero-lateral columns. Moreover, if there 

 were a gradual giving-off of Encephalic fibres from the longitudinal columns 

 into the roots of the nerves, the size of these columns ought progressively to 

 diminish from above downwards; whereas it is asserted by Volkmann, who has 

 strenuously upheld this doctrine, 3 that the size of the white columns presents 

 no such diminution, but that it is everywhere proportional to the quantity of 

 gray matter in the Cord. Thus in Serpents, the Spinal cord (as already no- 

 ticed) is remarkable for its uniformity of dimension through its entire length, 

 the absence of limbs preventing the necessity for an increase in the quantity of 

 gray matter in any part, and the fibrous columns presenting a similar uniformity 

 throughout; whereas, if the latter be really Encephalic, they should gradually 

 dwindle away from the head to the tail. Moreover, it has been estimated by 

 Volkmann, that the area of the whole Spinal Cord of a Boa, at its anterior part, 

 is not more than one-eleventh part of the united area of the 221 pairs of nerves 

 which are given off from it. Further, it is urged by Volkmann, that the white 

 columns are absolutely smaller in the cervical region than they are in the 

 lower part of the cord, so that they would not suffice to convey even the lumbar 

 columns upwards to the Encephalon, much less to transmit the fibres of all the 

 intervening nerves in addition. Thus, having weighed four pieces of a Horse's 

 spinal cord, all of the same length, and taken respectively from below the 

 second, eighth, nineteenth, and thirtieth pairs of nerves, he found that their 

 weights were respectively 219, 293, 163, and 281 grains; and that the trans- 

 verse sections of the gray matter gave respectively the area of 13, 28, 11, and 

 25 square lines, whilst those of the white matter measured 109, 142, 89, and 

 121 square lines. Hence the greatest amount of fibrous as well as of gray 

 substance is found in those enlargements of the cord which are the ganglionic 

 centres of tlie nerves of the extremities; these being the parts from which the 

 second and fourth segments were taken in the preceding experiment. On the 

 other hand, in the middle dorsal region, the amount of fibrous structure appears 



1 " Untersuclmngen iiber die Textur des Riickenmarks," Leipzig, 1842. 



2 "Physiological Anatomy and Physiology of Man," Am. Ed. 



3 See his valuable article " Nervenphysiologie," in Wagner's " Handworterbuch der 

 Physiologic." 



