RECAPITULATION AND PATHOLOGICAL APPLICATIONS. 217 



origin to its termination ; and it is not improbable that there are several distinct 

 endowment! in the different fibres composing each trunk. There is no evi- 

 dence that the fibrous structure serves any different purpose than that of a 

 mere conductor; and there seems good reason to believe that all the active 

 operations, of which the nervous system is the instrument, originate in the 

 gray matter. A mass of gray matter, connected with nervous trunks, forms 

 a ganglion. In the Invertebrata, the ganglia are frequently numerous, and 

 are scattered through the system, without much connection with each other- 

 each having a distinct function. In Vertebrated animals, on the other hand, 

 they are united into one mass partly, it would seem, for the sake of the 

 protection afforded them by the bony skeleton and partly in order that more 

 complete consentaneousness of action may be attained. Still, several distinct 

 divisions may be traced in the centres of the Cerebro-Spinal System partly 

 by the determination of their respective functions, as indicated by observation 

 and experiment and partly by the study of the distribution of the nerves 

 proceeding from them. In this manner we arrive at the knowledge of several 

 distinct ganglionic centres, of which the following may be considered as a 

 general account. 



I. The true Spinal Cord, consisting of a nucleus of gray matter, receiving 

 afferent fibres, and giving origin to efferent; by these it is connected with all 

 parts of the body, but especially with the surface and muscles of the extremi- 

 ties. The actions of this centre may be performed without consciousness on 

 the part of the individual; and they consist in the reflexion of a motor im- 

 pulse along. an efferent nerve, on the reception of a stimulus conveyed by an 

 afferent or excitor nerve. These reflex movements can be best excited when 

 the muscles are removed from the control of the Will, which otherwise gene- 

 rally antagonizes them. Some of them are connected with the maintenance 

 of the organic functions ; and others with the protection or withdrawal of the 

 body from injury. Muscular movements may also be excited, by a stimulus 

 directly applied to the Spinal Cord itself ( 157 212). 



II. The Medulla Oblongata, or cranial prolongation of the Spinal Cord. The 

 actions of this do not essentially differ from those of the true Spinal Cord; but 

 they are connected with different organs. This part consists chiefly of the 

 centres of the nerves of Respiration and Deglutition two functions, of which 

 the continual maintenance is essential to the life of the being; and it would 

 seem as if these were placed within the cranium, to be more secured from 

 accidental injury. The movements concerned in Respiration and Deglutition 

 are, like those excited through the true Spinal Cord, of a strictly reflex cha- 

 racter, oeing, in all instances, due to an impression, or stimulus, originating 

 in the periphery of the system, which, being conveyed to the centre, excites 

 there a motor impulse ; and they, also, are independent of Sensation ( 184 

 194). 



III. The ganglia of the nerves of Special Sensation, which form, as it 

 were^ the continuation of the Medulla Oblongata. These, also, appear to 

 minister to actions, which do not differ widely from the Reflex in character 

 being almost necessarily excited by certain stimuli, and being only in a degree 

 controllable by the will. But their actions differ in this, that they are attended 

 with consciousness, and also, it would appear, with certain peculiar feelings.' 

 Reasons have been given for the belief that these ganglia are the centres of 

 those actions which are commonly termed instinctive in the lower animals, 

 and consensual and emotional in ourselves. These all correspond in being 



formerly explained ( 112), there is probably never an actual termination of nervous 

 fibres, either in the muscles or in gray matter; but they cease to run in their previous 

 direction, after forming their terminal loops; and their course, as afferent or efferen, 

 fibres, may consequently be said to begin or to end at these points, 

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