FUNCTIONS OP THE SENSORY GANGLIA. 663 



relation of a sensory to a motor nerve-nucleus, it would almost? follow that 

 severe injury to the former would paralyze the latter by inhibitory influence, 

 even when the injury was confined to the Thalamus, and did not reach the 

 Corpus Striatuni directly or indirectly. Lastly, the experiments of M. Brown- 

 Sequard may be referred to, as showing that in the case of the Spinal Cord, 

 a very much more complete destruction of the gray matter is requisite to 

 destroy sensation entirely than is requisite for the abolition of the power of 

 motion. Dr. Broadbent considers that the partial character of the paralysis 

 may further be referred to the mode of functional activity of the muscles 

 affected as compared with those which escape, and believes it may be shown 

 that where the muscles of the corresponding parts on opposite sides of the 

 body constantly act in concert, and seldom if ever independently, the nerve 

 nuclei of these muscles are so connected by commissural fibres as to be pro 

 tanto a single nucleus. This combined nucleus will have a set of fibres from 

 each Corpus Striatum, and will usually be called into action by both ; but it 

 will also be capable of being excited by either siugly, though more or less 

 completely according as the commissural connection between the two halves 

 is more or less perfect. In support of this statement, it may be observed 

 that those muscles which are commonly associated in their movements like 

 the ocular muscles, are not paralyzed ; those of the cheek, on the other hand, 

 exhibit a degree of independence of action, and are slightly paralyzed ; and 

 lastly, the muscles of the arm and leg, which are almost completely inde- 

 pendent in their action, are most severely affected. It is fouud also that in 

 unilateral convulsion or spasm, the movements are bilateral in those parts 

 which escape paralysis in Hemiplegia i. e., the combined nucleus transmits 

 the irregular one-sided impulse aloug the nerves of both sides. 



532. In employing the information derived from the foregoing sources, as 

 a guide in the inquiry into the part performed by the Sensory Ganglia in the 

 ordinary operations of the Cerebro-Spinal system, we have to distinguish, as 

 in the case of the Spinal Cord, between their operation as independent 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 seat of Sensation (i. e., the material instruments 

 through which the consciousness becomes affected by 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 gener- 

 ally, 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 Organic life, being provided for by the excito-rnotor portion of the ap- 

 paratus, 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 ani- 

 mals 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 reasoning processes, which operate 

 upon the motor apparatus either emotionally or volitionally. And it is for 



