FUNCTIONS OF THE PAR VAGUM. 317 



sory roots ; and affirming that irritation of the roots of the Spinal 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 belong exclusively to each. Some 

 of the fibres usually considered to belong to the Spinal Accessory, are occa- 

 sionally seen to connect themselves with the roots of the Par Vagum, even 

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

 roots of the Spinal Accessory are chiefly motor, and those of the Par Vagum 

 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 Par 

 Vagum may thus derive additional motor fibres from the Spinal Accessory, 

 whilst it supplies that nerve with additional afferent fibres. In regard to its 

 trunk, there can be no doubt that the Par Vagum 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 capa- 

 ble of conveying those impressions which become sensations when commu- 

 nicated 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 impressions 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 im- 

 pressions 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 Glosso-pharyngeal ; whilst 

 the oesophageal 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 extraordinary circumstances. 



409. The section of the Par Vagum produces, as would readily be expected, 

 great disorder of the functions of Respiration and Digestion, to which it minis- 

 ters. It is an operation which has been very frequently performed ; and the 

 statements of its results vary considerably amongst each other, being generally 

 influenced, in some degree, by the preconceived views of the experimenter.* 

 The section of the Par Vagum, when practised with the view of ascertaining 

 the influence of the nerve upon the lungs and stomach, is usually made in the 

 neck, between the origins of the superior and inferior (or recurrent) laryngeal 

 branches. Hence the muscles of the larynx are paralyzed ( 379) ; and, if the 

 animal should struggle violently, the ingress of air is likely to be obstructed 

 by the flapping down of the arytenoid cartilages, and by the closure of the 

 glottis. This is especially the case in young animals, in which the larynx is 

 small. But in those that are full grown, and have a large larynx, an adequate 

 quantity of air may still find its way through the aperture, if the animal refrain 

 from any violent effort. In a considerable number of Dr. Reid's experiments, 

 therefore, he did not find it necessary to introduce the trachea-tube, which 

 other experimenters have generally employed ; an opening was made into the 

 trachea, however, in those instances in which, from any cause, the entrance of 

 air was obstructed. 



* The Author employs, as in his opinion the most worthy of confidence, the experiments 

 of Dr. J. Reid (Edinb. Med. and Surg. Journ., vols. xlix. and li.), on whose accuracy he has 

 strong personal reasons for placing reliance; and whose anatomical and pathological attain- 

 ments are such as to render him fully competent to the task. 



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