892 



PAR VAGUM. 



We believe that we are justified in concluding 

 from the evidence here adduced, that the vagus, 

 even at its origin, and before it has received 

 any fibres from the accessory, does contain a 

 few motor filaments.* 



We shall here make a few remarks upon tho 

 immediate effects of chemical and mechanical 

 excitation of the trunk of the vagus as it lies in 

 the neck, and then proceed to examine in detail 

 the functions of its auricular, pharyngeal, laryn- 

 geal, cesophageal, cardiac, pulmonary, and gas- 

 tric branches. When the trunk of the vagus 

 has been exposed in the neck in a living animal, 

 and is cut, bruised, or rendered suddenly tense 

 by forcible stretching, the animal generally 

 gives indications of severe suffering, while in 

 some cases the animal remains quiescent, and, 

 as far as we can judge, suffers little, if any. 



There can be no doubt, from the distinct 

 testimony of numerous experimenters, + that 

 the trunk of the vagus does contain sensiferous 

 filaments, but there are good grounds for be- 

 lieving that the application of chemical agen- 

 cies or the infliction of mechanical injuries 

 upon this nerve below the origin of its superior 

 laryngeal branch, are not attended with the 

 same amount of pain as would attend similar 

 lesions of one of the ordinary spinal nerves. 

 Dr. Marshall Hall and Mr. Broughton re- 

 marked, that when the compression of this 

 nerve is continued " for a few moments, an act 

 of respiration and deglutition follows, with a 

 tendency to struggle and cough." J Komberg 

 observed excitation of the vagus in the neck in 

 a horse produce cough ; and it appears that 

 Cruveilhier had made previously the same ob- 

 servation. || In some of the cases in which I 

 made this experiment on dogs, I observed 

 powerful respiratory muscular movements, but 

 never succeeded in inducing cough. Longet 

 has been equally unsuccessful in producing 

 cough by this means.^I The respiratory mus- 

 cular movements which follow excitation of the 

 vagus in the neck are not dependent upon any 



* The opinion that the internal branch of the 

 spinal accessory furnishes no motor filaments to the 

 trunk of the vagus has been several times of late 

 attributed to me. That this is a mistake, any one 

 may satisfy himself by reading the account which I 

 have given of these experiments, from which I 

 drew the following conclusions. " That the inter- 

 nal branch of the spinal accessory assists in moving 

 the muscles of the pharynx we are satisfied, not 

 only from the experiments just stated, but also 

 from those upon the pharyngeal branch of the par 

 vaqum. Of the probable destination and functions 

 of the other filaments of the internal branch of the 

 accessory, we cannot pretend to judge without more 

 extended inquiries. We certainly do not consider 

 that these experiments entitle us to assert that they 

 are not motor filaments." Edinburgh Medical and 

 Surgical Journal, vol. 173, 1838. 



t We have elsewhere collected the statements 

 of different authors on this point. (Edin. Med. & 

 Surgical Journal for 1838-9.) 



t Transactions of the British Scientific Associa- 

 tion, vol. iv. p. 677. 



Miiller's Archives for 1838. 



|| Nouv. Biblioth. Med. t. ii. p. 172, 1828, as 

 quoted by Longet. 



If Anatomie et Physiologic du Systeme Nerveux, 

 &c. t. ii. p. 309. 



direct action transmitted downwards to the 

 lungs or muscles of respiration, but upon a 

 reflex action, as Dr. Marshall Hall pointed out, 

 arising from certain impressions being carried 

 upwards to the medulla oblongata by the inci- 

 dent fibres of the vagus, followed by the trans- 

 mission of a motor influence outwards from 

 this portion of the central organ of the nervous 

 system along the motiferous nerves distributed 

 in the muscles moved. The excitation and 

 mechanical injury of the vagus in the neck in- 

 duces various other results, some of which may 

 be included among their immediate effects, such 

 as those upon the movements of the intrinsic 

 muscles of the larynx, the diminution of the 

 frequency of the respirations, &c. ; but these 

 will be more methodically introduced among 

 the remarks which we have to make upon the 

 functions of the individual branches of the 

 nerve.* 



Auricular branch. From the origin of this 

 branch from the superior ganglion of the vagus, 

 and from being partly distributed to the inte- 

 guments of the pavilion of the external ear, it 

 is probable that it is composed of sensiferous 

 filaments. If the portion of this branch which 

 throws itself into the portio dura be sensiferous, 

 the portio dura may contain some sensiferous 

 filaments as it issues from the stylo-mastoid 

 foramen. f 



Phuri/ngeal branches. As a great part, some- 

 times nearly the whole, of the superior pharyn- 

 geal branch of the vagus comes directly from the 

 internal branch of the spinal accessory, we 

 may, on anatomical grounds alone, conclude 

 that it contains motor filaments. In irritating 

 this branch in dogs, both alive and immediately 

 after death, we observed extensive movements 

 of the muscles of the pharynx and soft palate 

 without any distinct indications of pain. As, 

 however, the animal must necessarily be sub- 



* In some animals, as in the dog, the division or 

 compression of the vagus in the neck is immedi- 

 ately followed by diminution of the pupil of the eye 

 of that side, the protrusion of the cartilaginous 

 membrane at the inner cauthus over the inner part 

 of the anterior surface of the eyeball, the retraction 

 of the eyeball deeper into the socket, and a slight 

 approximation of the eyelids ; and subsequently by 

 inflammation of the conjunctiva. Petit (Histoire 

 de 1'Academie Royale des Sciences, annee 1727) 

 was the first who observed these effects, and justly 

 attributed them to injury of the sympathetic nerve. 

 It is only in those animals in which the sympathe- 

 tic joints itself to the vagus in the upper part of the 

 neck, that the division or compression of the trunk 

 of the vagus produces any change on the eye. Vide 

 Ediu. Med. and Surgical Journal, No. 140, for ex- 

 periments on this subject by the author of this arti- 

 cle, and Valentin's Treatise de Functionibus Nerv. 

 Cereb. &c. p. 109. 



t Arnold believes that the sympathy occasionally 

 observed between the external ear and the lungs 

 may be owing to this auricular branch of the vagus. 

 He refers to some cases, where the presence of 

 hardened cerumen, of a bean, of a pea, and other 

 foreign bodies in the cartilaginous tube of the ex- 

 ternal ear, has induced long-continued cough and 

 even vomiting. (Bemerkungen uber den Baue des 

 Hirns nnd Ruckenmarks, &c. S. 168. Zurich, 1838.) 

 In some individuals coughing can readily be in- 

 duced by irritating the inner surface of the mcatus 

 auditorius cxternus. 



