690 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



and Bernard) are opposed to this opinion ; maintaining that the Pneumogastric 

 has motor roots of its own ; and affirming that irritation of the roots of the Spi- 

 nal Accessory produces little or no effect on the muscles supplied by the trunk 

 of the Par Vagum. The fact appears to be that the roots of these two nerves 

 are so commingled, that it is difficult to say what belongs exclusively to each. 

 Some of the fibres usually considered to belong to the Spinal Accessory are 

 occasionally seen to connect themselves with the roots of the Pneumogastric, 

 even before the ganglion is found upon it. And it seems most probable that, 

 while the roots of the Spinal Accessory are entirely motor, those of the Pneu- 

 mogastric are chiefly afferent ; that they inosculate with each other, in a degree 

 which may vary in different species, and even in different individuals ; and that 

 the Pneumogastric may thus derive additional motor fibres from the Spinal Acces- 

 sory, whilst it supplies that nerve with afferent fibres. Further, from the re- 

 searches of M. Cl. Bernard, to be presently noticed ( 719), it appears probable 

 that the motor fibres properly belonging to the Pneumogastric are adequate to 

 the regulation of those movements of the larynx and other portions of the air- 

 passages, which are concerned in the passive act of Respiration. In regard to 

 its trunk , there can be no doubt that 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 sensations 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 have of an abnormal condition of the 

 organs which it supplies. Thus, the suspension of the respiratory movements 

 gives rise to a feeling of the greatest uneasiness, which must be excited by im- 

 pressions conveyed through this nerve from the lungs ; and an inflamed state of 

 the walls of the air-passages causes the contact of cold and dry air to produce 

 distressing pain and irritation. Yet of the ordinary impressions conveyed from 

 these organs, which are concerned in producing the respiratory movements, and 

 in regulating the actions of the glottis, we are not conscious. The same may 

 be said of the portion of the nerve distributed upon the alimentary tube. The 

 pharyngeal branches are almost exclusively motor, the afferent function being 

 performed by the Grlosso-pharyngeal; whilst the cesophageal and gastric are both 

 afferent and motor, conveying impressions which excite reflex movements in the 

 muscles of those parts, but which do not become sensations except under extra- 

 ordinary circumstances. The participation of this nerve in the operations of 

 Deglutition, Digestion, Circulation, and Respiration, and the effects of injury to 

 its trunk or branches, have already been considered in the account of those 

 functions. 



719. In regard to the functions of the Spinal Accessory nerve, also, there 

 has been great difference of opinion; the peculiarity of its origin and course 

 having led to the belief that some very especial purpose is answered by 

 it. The roots of this nerve arise from the side of the Spinal Cord as low down 

 as the 5th or 6th cervical nerve j and the trunk formed by them ascends into 

 the cranium between the anterior and posterior roots of the spinal nerves. 

 From the recent researches of Mr. J. L. Clarke, 1 it appears that these roots 

 may be traced into a special tract of vesicular matter, which descends as far as 

 the lumbar enlargement. The predominance of motor fibres in its roots, its 

 inosculation with the Pneumogastric, and its probable reception of sensory 

 fibres from the latter whilst imparting to it motor filaments, have been already 

 referred to ( 718). As its trunk passes through the foramen lacerum, it 

 divides into two branches; of which the internal, after giving off some filaments 



1 " Philosophical Transactions," 1851, p. C13. 



