PAR VAGUM. 



001 



mucous secretions were not poured out from the 

 inucous surface of the stomach and intestines, 

 though it presented the inflammation usual in 

 such cases.* We have carefully repeated these 

 experiments, and obtained different results. The 

 quantity of watery and mucous secretions was 

 nearly the same in animals after the vagi had been 

 divided, as in animals upon which this operation 

 had not been performed.f These experiments 

 upon the eHiects of lesion of the vagi upon the dif- 

 ferent secretions poured out from the inner sur- 

 face of the digestive canal, though they do not 

 prove that the function of secretion is indepen- 

 dent of the nervous system, seeing that nume- 

 rous filaments of the sympathetic nerve are also 

 distributed there, are yet sufficient to neutralize 

 the evidence drawn from the effects of lesion of 

 the vagi upon these secretions adduced by 

 those who maintain that secretion is dependent 

 upon the nervous system. 



Effects of lesion nf the vagi upon the 

 rapidity of absorpt ion from the, inner surface of' 

 the. stomach. It has been stated by DupuyJ 

 and Brachet, that the most active poisons in- 

 troduced into the stomach after division of the 

 vagi in much larger quantities than usual, pro- 

 duce their effects much more slowly. On the 

 other hand Mu'ller mentions that in thirty ex- 

 periments on Mammalia performed under his 

 direction by M. Wernscheidt, "not the least 

 difference could be perceived in the action of 

 narcotic poisons introduced into the stomach, 

 whether the nervus vagus had been divided on 

 both sides or not, provided the animals were of 

 the same species and size." We have made 

 several comparative experiments on this point, || 

 and obtained results which agreed nearly with 

 those mentioned by Miiller. 



The following short summary contains the 

 principal conclusions founded upon the facts 

 and observations above detailed, at which we 

 have arrived regarding the functions of the 

 nervus vagus. 



1. Though the trunk of the nervus vagus at 

 its attachment to the encephalon principally 

 consists of sensiferous and incident filaments, 

 it yet contains a few motor filaments. The 

 motor filaments contained in some of the 

 branches of the vagus chiefly come from the 

 spinal accessory. 



2. The filaments of the auricular branch of 

 the vagus are sensiferous and incident. 



2. The pharyngeal branches of the vagus are 

 principally if not entirely motor, and move the 

 muscles of the pharynx and soft palate in 

 obedience to certain impressions made upon 

 the incident filaments of the glosso-pharyngeal 

 and fifth pair of nerves distributed upon the 

 mucous surface of these organs. 



4. The superior laryngeal branch is chiefly 

 composed of sensiferous and incident filaments 

 which are abundantly distributed upon the 



* Philos. Trans., 1812, p. 102. 

 t Opus cit. for 1839, vol. li. 

 J Opus cit. p. 366. 

 $ Opu< cit. p. 186. 



[| MUller's Elements of Physiology, translated by 

 Baly, vol. i. p . 263, 2nd edit. 

 If Opus cit. vol. li. 



muco,us surface of the larynx, and much more 

 sparingly upon the inner surface of the lower 

 part of the pharynx. The few motor filaments 

 contained in the superior laryngeal are dis- 

 tributed in, and move the crico-thyroid muscle. 

 When the superior laryngeal branches are 

 divided or tied, every excitation of the inner 

 surface of the larynx fails to excite sensation, 

 or any reflex and muscular movement, and the 

 two crico-thyroid muscles are paralysed. 



5. The inferior lan/ngeal or recurrent 

 brunch is ramified in, and regulates the move- 

 ments of all the muscles attached to the aryte- 

 noid cartilages, viz. the crica-arytenoideus pos- 

 ticus and lateralis, the thyro-arytenoideus, and 

 the arytenoidei. The inferior laryngeal also 

 furnish the sensiferous filaments to the upper 

 part of the trachea, a few to the mucous surface 

 of the larynx, and still fewer to the pharynx. 

 The sensiferous filaments of the inferior laryn- 

 geal are, however, few in number and do not 

 impart much sensibility to the parts in which 

 they are distributed, presenting a striking con- 

 trast in this respect to the superior laryngeal. 

 When the inferior laryngeal is cut or tied, the 

 muscles attached to the arytenoid cartilages are 

 no longer moved voluntarily as in speech, or 

 involuntarily as in the muscular movements of 

 respiration ; and the arytenoid cartilages may 

 be mechanically carried inwards by the cur- 

 rents of air rushing into the lungs, so as to shut 

 up the superior aperture of the larynx and pro- 

 duce suffocation. When any excitation is 

 applied to the inner surface of the larynx in the 

 healthy state, this does not produce the con- 

 traction of the muscles which approximate the 

 arytenoid cartilages by acting directly upon 

 them through the mucous membrane ; but this 

 muscular contraction is effected indirectly and 

 by a reflex action, in the performance of which 

 the superior laryngeal acts as the incident or 

 afferent nerve, and the inferior laryngeal as the 

 motor or efferent nerve. It is also probable 

 that these filaments of the inferior laryngeal 

 distributed in the muscular fibres of the trachea 

 are motor. The inferior laryngeal branch is the 

 principal nerve of phonation, and when para- 

 lysed the voice becomes very faint. The 

 effects of the paralysis of the superior laryngeal 

 upon the voice are much less marked and are 

 much more doubtful. 



5. The asophageal branches of the vagus are 

 partly afferent and partly efferent nerves. In 

 some animals, as in the rabbit, the section of 

 the vagi in the neck is followed by the sus- 

 pension of the movements of the oesophagus 

 during deglutition, and the food is no longer 

 conveyed along it in the usual manner. This 

 lesion of the vagi does not produce these effects 

 by destroying the contractility of the muscular 

 fibres of the oesophagus, but by breaking the 

 continuity of the nervous circle necessary for 

 the accomplishment of all reflex movements. 

 In some other animals, as in the dog, the food 

 is still propelled along the oesophagus after 

 section of the vagi, so that it is probable that in 

 these animals the muscular fibres of the oeso- 

 phagus are also called into contraction by direct 

 excitation. 



