

FUNCTIONS OP THE SENSORY GANGLIA. 719 



ganglionic matter of the Spinal Cord, bears to that of the fibres which pass on 

 to the Sensorium, is not constant, but is liable to variation ; the former pre- 

 dominating in the Par Vagum and the G-losso-pharyngeal, whilst the latter are 

 more numerous in the Fifth Pair, and in most of the Spinal nerves. 



746. To the reflex actions of the Sensory Ganglia, all the motor fibres of the 

 Cranio-spinal axis, save those which originate in its Spinal portion, may be 

 considered as subservient; for, as we have seen, the motor columns from which 

 proceed the anterior roots of the Spinal nerves and the motor Encephalic nerves, 

 pass up into the Corpora Striata and Corpora Quadrigemina ; and although the 

 direct connection of the other ganglia of Special sense with the motor columns 

 is at present a matter of presumption only, yet this presumption is strongly 

 supported by the analogy of the Optic ganglia, the distinctness of the connection 

 in this case being easily accounted for, when it is remembered in how great a 

 degree the general movements of the body are guided by the visual sense. This 

 anatomical evidence is fully borne out by the results of experiment ; since, as 

 we have seen ( 738), convulsive movements of all parts of the body may be 

 excited by the application of the electric stimulus to this division of the 

 Encephalic centres. 



747. Functions of the Sensory Ganglia. We have now to consider what 

 deductions may be drawn with regard to the functions of the Sensory Ganglia 

 in Man, from the facts supplied by Comparative Anatomy, Experimental inquiry, 

 and Pathological phenomena. Here, as in the case of the Spinal Cord, we have 

 to distinguish between their operation as independent ganglionic centres, and 

 their action in subservience to the Cerebrum, which is superposed upon them. 

 We have seen reason to conclude that, in their former capacity, they are to. be 

 regarded as the true centres of Sensation (i. e. of the consciousness of external 

 impressions), and as the instrument, in virtue of their own " reflex" power, of 

 that class of Instinctive or Automatic movements, which require to be prompted 

 and guided by sensations, and which cannot, therefore, be referred to the excito- 

 motor group. But although it is sufficiently obvious that such movements 

 constitute the highest manifestations of Animal life in the Invertebrata generally, 

 and that they are but little modified by any higher principle of action even in 

 the lower Vertebrata, yet it is no less obvious that in adult Man, in whom the 

 Intelligence and Will are fully developed, we have comparatively little evidence 

 of this independent reflex action of the Sensory Ganglia; all those automatic 

 actions which are immediately necessary for the maintenance of his Orgaadc life 

 being provided for by the excito-motor portion of the apparatus, so that, although 

 sensation ordinarily accompanies most of them, it is not essential to them; 

 whilst those which are necessary to provide more remotely for its requirements are 

 for the most part committed to the guidance of his Reason. For the impressions 

 which have been brought by the afferent nerves to his Sensorium, and which 

 have there produced sensations, do not in general react at once upon the motor 

 apparatus (as they do in those animals in which the Sensory Ganglia are the 

 highest of the nervous centres), but usually transmit their influence upwards to 

 the Cerebrum, through whose instrumentality they give rise to ideas and reason- 

 ing processes, which operate upon the motor apparatus either emotionally or 

 volitionally. And it is for the most part only when this upward transmission 

 is checked, either by the non-development or the functional inactivity of the 

 Cerebrum, or by its complete occupation in some other train of action or, on 

 the other hand, when the reflex action of the Sensory ganglia is called into play 

 with unusual potency that we have any manifestations of the sensori-motor or 

 consensual mode of operation in Man, at all comparable in variety or importance 

 to those which are so remarkable in the lower animals. 



748. Still, sufficient evidence of the existence of this class of reflex move- 

 ments may be drawn from observation of the actions of Man in his ordinary 



