CEREBRO-SPINAL NERVOUS CENTRES IN GENERAL. 565 



movements, which are executed in respondence to certain promptings con- 

 veyed to them through their sensorium. Now between the complete want of 

 this; controlling power of the Will, and the most perfect |ossr<sion of it, every 

 intermediate gradation is presented by the several individuals which make 

 up the Human species; some persons being so much accustomed, in conse- 

 quence of the weakness of their Will, to act directly upon the prompting of 

 every transient impulse', that they can scarcely be said to be voluntary agents; 

 and others allowing certain dominant ideas or habitual feelings to gain such 

 a mastery over them, as to exercise that determining power which the Will 

 alone ought to exert. This gradation may be perfectly traced in children, 

 in whose education the development of the faculty of "self-control " should 

 be a leading .object ; audit is also displayed in certain phases of mental 

 Imbecility, which result from a deficiency of the power of voluntarily fixing 

 the attention upon any object of consciousness, and of thus withdrawing it 

 either from external objects that tend to distract the mind, or from notions 

 it has adopted which hold it in subjection. 



452. When we apply ourselves to the study of the Cerebro-Spinal Nervous 

 centres of Man, we find ourselves peculiarly liable to be misled by the great 

 development which the Cerebrum presents, both as to size and to complexity 

 of structure, in proportion to the other centres; and thus it has happened 

 that, through the too exclusive attention commonly paid to Hainan Anatomy, 

 the meaning of the facts brought to light by dissection has been very com- 

 monly misapprehended, and 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 com- 

 parison with both extremes, that it is possible to establish what are its fun- 

 damental or essential, and what its accessory parts ; and in this way only 

 can such a correspondence be established between the development of a par- 

 ticular structure and the manifestation of a 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 " experi- 

 ments ready prepared for us by Nature" is so much above that of the results 

 of artificial mutilations. 



453. Cerebro-Spinal Nervous Centres. Under the guidance, then, of these 

 principles, we find that we may distinguish, as the fundamental part of the 

 Cerebro-Spinal apparatus of Man, the Oranio-Spinal Axis, consisting of the 

 Spinal Cord, the Medulla Oblongata, and the Sensory Ganglia, and alto- 

 gether constituting the centre of automatic movement. The Spinal Cord, 

 consisting of a tract of vesicular matter inclosed within strands of longitudi- 

 nal fibres, and giving off successive pairs of intervertebral nerves which are 

 connected at their roots with both of these components, is obviously homolo- 

 gous with the gangliated ventral column of the Articulate, chiefly differing 

 from it in the continuity of the ganglionic substance which occupies its inte- 

 rior; and each segmental division of it, which serves as the centre for its own 

 pair of nerves, may be considered, like each ganglion of the ventral column 

 of the Articulata, as a repetition of the single " pedal " or locomotive gan- 

 glion of the Mollusca. The Medulla Oblongata consists of a set of strands, 

 which essentially correspond with the cords that pass round the oesoph- 

 agus in Invertebrated animals, connecting the cephalic ganglia with the first 

 suboesophageal ganglion ; but as the whole cranio-spiual axis in the Verte- 

 brata lies above the alimentary canal (the trunk being supposed to be in a 

 horizontal position), there is no such divergence of these strands, the only 



