GENERAL SUMMARY. 645 



its fundamental and essential part; for not only is it the instrument of all 

 those actions which are directly excited by sensations or impressions derived 

 from without, many of these being necessary to the maintenance of his organic 

 functions; but it is also the connecting link between the Cerebrum and the 

 external world. For, as will appear hereafter, the Cerebrum receives all its sti- 

 mulus to action through the sensorial ganglia, to which all the proper sensory 

 nerves are traceable; whilst on the other hand, in carrying into effect the 

 mandates of the will, it does not operate directly upon the muscles, but affects 

 them through the instrumentality of the Automatic motor apparatus. 



677. The dominant character of the Nervous System in Yertebrated animals 

 is marked by the subserviency of the whole organism to its purposes. In a 

 large proportion of the Invertebrata, the Nervous system seems like an append- 

 age to the rest of the structure, a mechanism superadded for the sake of 

 bringing its various parts into more advantageous relation; and we do not find 

 any special adaptation of the organs of support for its protection. But in all 

 the Vertebrated classes, we find that the internal osseous skeleton, whose exist- 

 ence supplies the most distinctive character of the group, is adapted not merely 

 to furnish the most complete and efficient protection to the Nervous centres, 

 but also to afford points of attachment to the Muscles, as well as a system of 

 inflexible levers on which they may exert the contractile power called forth by 

 the nerves; so that the development of the neuro-skeleton (thus designated in 

 contradiction to the dermo-skeleton) has a constant relation to that of the Nervo- 

 muscular apparatus. This is most remarkably seen in Man; in whom the 

 "archetype" or fundamental plan of the Vertebral skeleton is most departed from, 

 in order that it may be adapted to his special requirements. 1 And it is in him, 

 too, that the Nervous system presents the greatest proportionate development, 

 and that, by the intimate connections which subsist between its several parts, it 

 is made so far to constitute one whole, that the determination of their respective 

 functions is attended with the greatest difficulty. It has been, in fact, through 

 the too exclusive attention commonly paid to Human Anatomy, that the mean- 

 ing of the facts brought to light by dissection has been very commonly misap- 

 prehended; and that many of the physiological interpretations based upon them, 

 have been completely negatived by more extended inquiry. It is only, in fact, 

 by studying the Cerebro-Spinal apparatus in its lowest, as well as in its highest 

 form, and by bringing the intervening grades into comparison with both extremes, 

 that it is possible to establish what are its fundamental or essential, and what its 

 accessory parts ; and in this way only can such a correspondence be established 

 between the development of a particular structure, and the manifestation of a 

 certain psychical endowment, as may enable the latter to be attributed with any 

 degree of probability to the former. In fact, there is no part of the Human 

 Organism, as to which the advantages of such a comparison are, so striking, or 

 in which the value of the " experiments ready prepared for us by Nature" is so 

 much above that of the results of artificial mutilations. 



678. Under the guidance, then, of these principles, we find that we may 

 distinguish, as the fundamental part of the Nervous system of Man, the 

 Cranio- Spinal Axis, consisting of the Spinal Cord, the Medulla Oblongata, and 

 the Sensory Ganglia, and altogether constituting the centre of automatic move- 

 ment. The Spinal Cord, consisting of a tract of vesicular matter inclosed 

 within strands of longitudinal fibres, and giving off successive pairs of inter- 

 vertebral nerves which are connected at their roots with both of these components, 

 is obviously homologous with the gangliated ventral column of the Articulata, 

 differing from it only in the continuity of the ganglionic substance which occupies 



1 See "Princ. of Phys., Gen. and Comp.," g 326, k, Am. Ed. 



