65 NERVOUS SYSTEM. 



The first of these conditions is easily fulfilled. All that is necessary is to stimulate 

 the roots before the nerves have received any anastomosing filaments. To avoid contrac- 

 tions of muscles due to reflex action, it is hest to divide the roots and to stimulate their 

 distal portion. If it he true that stimulation of the distal extremities of the roots the 

 irritation so applied as not to involve communicating filaments from motor nerves, and 

 not to be conveyed to the centres, producing reflex movements through other nerves 

 does not produce any movements, it is fair to assume that the true filaments of origin are 

 exclusively sensory. The facts upon this point demand careful and critical study ; and it 

 will be proper to discard the earlier experiments, made before the mechanism of reflex 

 action had been satisfactorily established. 



If the experiments of Longet be accepted without reserve, they prove as conclusively 

 as is possible without exposing the roots in living animals, an operation which is imprac- 

 ticablethat the true filaments of origin of the pneumogastrics are* exclusively sensory, 

 or, at least, that the nerve contains no motor filaments except those derived from other 

 nerves. The following quotation gives the essential points in these experiments : 



" In dogs of large size and in horses, I have isolated in the cranium, with the most 

 minute care, the pneumogastric of the medulla oblongata and the superior filaments of 

 the spinal accessory (internal branch), in order to avoid all reflex movement and any 

 derivative current upon the last-named nerve ; I then immediately caused the current to 

 act exclusively upon the filaments of origin of the pneumogastric, without having ever 

 seen the'slightest contraction supervene, either in the muscles of the larynx or pharynx, 

 or in the muscular tunic of the oesophagus, or elsewhere. 



"But also I have never failed to demonstrate to all those who witnessed my experi- 

 ments, how it is easy to obtain opposite results in neglecting only one precaution : it 

 suffices, for example, to slightly moisten the slip of glass or oiled silk which serves to 

 isolate the two nerves, in order that the current should act immediately upon the superior 

 filaments of the spinal accessory, from which we have marked contractions in the organs 

 just mentioned." 



These experiments seem entirely conclusive. In treating of the reflex phenomena of 

 deglutition and their relations to the superior branches of the pneumogastric, the pharyn- 

 geal, and the superior laryngeal, it will be seen that irritation, either of these nerves or 

 of the mucous membranes to which they are distributed, will produce contractions in the 

 muscles. All who are practically familiar with the application of electricity to the nerves 

 know how difficult it is to insulate the nervous trunks so as to avoid the influence of 

 "derived" currents. In carefully studying the experiments of Longet, it seems that all 

 the physiological conditions were fulfilled ; and that, when the nerve is divided at the 

 root and the stimulation is applied to the peripheral end, so as to cut off all reflex action 

 from the nervous centres, and when sufficient care is exercised to prevent the propagation 

 of the current to the motor connections of the pneumogastric, the nerve, from its origin 

 at the medulla oblongata to the ganglion of the root, contains no motor filaments and is 

 exclusively sensory. We shall therefore adopt, without reserve, the conclusions of Longet, 

 that the true filaments of origin of the pneumogastrics are exclusively sensory, or, at least, 

 that they have no motor properties. 



Properties and Functions of the Auricular Nerves. There is very little to be said 

 with regard to the auricular nerves, after the description we have given of their anatomy. 

 They are sometimes described with the facial and sometimes with the pneumogastric. 

 1 hey contain filaments from the facial, the pneumogastric, and the glosso-pharyngeal. 

 The sensory filaments of these nerves give sensibility to the upper part of the external 

 auditory meatus and the membrana tympani. 



Properties and Functions of the Pharyngeal Nerves. The pharyngeal branches of 

 the pneumogastric are mixed nerves, their motor filaments being derived from the spinal 



