728 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



for the volitional and for the automatic movements ; since it is not readily to be 

 conceived how a set of movements originally performed by the one, can ever 

 be transferred to the other ; whilst, on the other hand, it is easy to understand 

 how the same motorial action may be excited in the automatic centres, either 

 by an external impression conveyed thither by an afferent nerve from a Sensory 

 surface (as that of the irritation in the air-passages, which excites the act of 

 coughing), or by a stimulus proceeding from the convoluted surface of the Cere- 

 brum, and conveyed along those connecting fibres which Reil with great sagacity 

 termed the ''nerves of the internal senses/' 



759. To sum up, then, we seem justified in concluding that the Cranio- Spinal 

 Axis of Man and other Vertebrata consisting of the Sensory Ganglia, Medulla 

 Oblongata, and Spinal Cord is (like the chain of cephalic and ventral ganglia 

 of Articulata with which it is homologous) the immediate instrument of all sen- 

 sorial and motor changes; that by its sole and independent action are produced 

 all those movements which are ranked as automatic or instinctive, these being 

 performed in respondence to external impressions which may or may not affect 

 the consciousness ; but that when acting in subordination to the Cerebrum, the 

 Cranio-Spinal Axis transmits upwards to it the influence of Sensorial changes, 

 and receives from it the downward impulses, which it directs automatically into 

 the appropriate channel for the execution of the movements which the Mind has 

 directed. The number of purely automatic actions diminishes in proportion to 

 the development of the Cerebrum, and to the subjection of the Automatic ap- 

 paratus to its control ; but even in Man, those most closely connected with the 

 maintenance of the organic functions, or most necessary for the conservation of 

 the bodily structure, remain quite independent of any mental agency, and most of 

 them do not require consciousness for their excitation. But when the activity of 

 the Cerebrum is suspended or is otherwise directed, without any affection of the 

 automatic apparatus, movements which have long been habitually performed in 

 a particular sequence, may be kept up, when the will has once set them in action, 

 through the automatic mechanism alone ; the impressional or sensational change 

 produced by each action supplying the stimulus which calls forth the next. It 

 may further be concluded that the Sensory Ganglia, which are the instruments 

 whereby we are rendered conscious of external impressions, are also the seat of 

 those simple feelings of pleasure and pain which are immediately linked on to 

 that consciousness. For it can scarcely be doubted that such feelings must be 

 associated with particular sensations, in animals that have no ganglionic centres 

 above these ; since we must otherwise regard the whole series of Invertebrated 

 tribes as neither susceptible of enjoyment, nor capable of feeling pain or dis- 

 comfort. And it is scarcely probable that a state of consciousness which we can 

 scarcely ourselves distinguish from the sensation that induces it should have a 

 separate centre in our Encephalon. 



4. Of the Cerebellum, and its Functions. 



760. The Cerebellum is an organ which, though confined to the Vertebrated 

 sub-Kingdom, is yet in peculiarly intimate relation with tHe Automatic appa- 

 ratus. In that highest state of development which it presents in Man, we find 

 it to consist of two lateral lobes or hemispheres, composed of nerve-fibres invested 

 in a very peculiar manner by vesicular substance, and of a central lobe, also 

 containing a combination of the vesicular and fibrous substances, which is known 

 under the designation of the " vermiform process/' The hemispheres are not 

 only connected with each other by this central lobe, but also by the fibrous com- 

 missure which passes beneath the Medulla Oblongata, and is known as the 

 " Pons Varolii." The commissural fibres form part of the " Crura Cerebelli ;" 

 but another portion is formed by the strands which connect the Cerebellum with 



