622 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



acter, result from the irritation ; and strong evidence of their sensibility are 

 also given. It has been further asserted that, when the roots of the Spinal 

 Accessory nerve are irritated, no indications of sensation are given ; but that 

 the muscular parts supplied by the Pueumogastric, as well as by its own 

 trunk, are made to contract, even when the roots are separated from the 

 nervous centres ; so that these roots must be regarded as the channel of the 

 motor influence transmitted to them from the Medulla Oblongata. Where 

 the Pneumogastric swells into the jugular ganglion, an interchange of fibres 

 takes place between it and the Spinal Accessory ; and it seems clear that the 

 pharyngeal branches, which are among the most decidedly motor of all those 

 given off from the Pneumogastric, may in great part be traced backwards 

 into the Spinal Accessory. But, on the other hand, an equally numerous and 

 trustworthy set of experimenters (among whom may be mentioned J. Reid, 

 Miiller, Volkmanu, Stilling, Wagner, Chauveau, 1 and Bernard 2 ) are opposed 

 to this opinion ; maintaining that the Pneumogastric has motor roots of its 

 own ; and affirming that irritation of the roots of the Spinal Accessory pro- 

 duces little or no effect on the muscles supplied by the trunk of the Par 

 Vagum. In the careful experiments of MM. v. Kempen and Thiernesse, 3 

 the causes of these discrepancies have been elucidated, for they have shown 

 that if irritation be applied to the roots of either Spinal Accessory or Pueu- 

 mogastric nerves, contractions occur in the oesophagus, in the constrictor 

 muscles of the pharynx, and in the internal muscles of the larynx; and in 

 addition, when the Spinal Accessory roots are irritated, in the trapezius 

 and sterno-mastoid muscles. If, however, the roots of the Pneumogastric 

 nerves be divided, and irritation be again applied to the roots of the Spinal 

 Accessory, no movements are observed except in the trapezius and sterno- 

 mastoid muscles. Hence it would appear that in the former instance, the 

 oasophageal and laryngeal movements were occasioned by a reflex action 

 conveyed to the Medulla Oblongata by centripetal or sensory fibres in the 

 Spinal Accessory, and reflected down to the muscles by motor fibres in the 

 Pneumogastric nerves, the communication between the two nerves being 

 effected by a chain of gangliouic nerve-cells in the Medulla. This view 

 receives strong confirmation from another series of experiments performed 

 by M. v. Kempen, who found that if the supposed communication in the 

 Medulla between the two nerves were divided by a transverse section carried 

 between their respective origins, irritation of the posterior cut surface of the 

 Medulla or of the roots of the Spinal Accessory was only followed by move- 

 ments in the sterno-mastoid and trapezius muscles; whilst, when the same 

 irritation was applied to the upper extremity of the Medulla or to the 

 roots of the Pneumogastric, contractions occurred in the muscles of the 

 pharynx and larynx. Hence we may conclude that the Pneumogastric itself 

 contains the motor fibres which act on the muscles of the pharynx, cesopha- 

 gus, and larynx; although it probably receives additional motor fibres from 

 the Spinal Accessory, and supplies that nerve with afferent fibres. 



I"."). There can be no doubt that the trti.uk of the Pneumogastric is to be 

 considered as a nerve of double endowments; although it is certain that 

 these endowments are very differently distributed amongst its branches. 

 That the nerve is capable of conveying those Impressions which become sen- 

 xutiuns when communicated to the sensorium, is experimentally proved by 

 the fact, that, when its trunk is pinched, the animal gives signs of acute 

 pain; but it is also evident from the painful consciousness we occasionally 



1 Cliuuvrau, Journal do Physiologic, ISO'J, pp. I'.H) and '203. 



2 Bernard, Reeherches Experiment, sur Ics Functions da Norf Spinal, etc., 1844, 

 p. 30. 



3 Bulletin do PAcad. Roy. de Med. do Belgique, 18(33, torn, xvi, p. 184. 



