886 



PAR VAGUM. 



geus) upon the lateral surface of the pharynx. 

 (See article GLOSS-PHAKYNGEAL NERVE.) 



Superior laryngeul brunch (rctmun laryngem 

 superior) arises from the inner side of the 

 vagus, about four or five lines below the 

 superior pharyngeal branch, and from the upper 

 and inner part of the second or inferior ganglion. 

 It is considerably larger than the pharyngeal 

 branch, and in the first part of its course pro- 

 ceeds almost directly inwards, then inwards 

 and downwards, passing behind the internal 

 carotid and in front of the longus colli muscle.* 

 While it is behind the carotid it generally 

 divides into its two branches, the internal and 

 external. The internal is much the larger and 

 more important, crosses the lateral part of the 

 middle constrictor of the pharynx obliquely 

 downwards, forwards, and inwards, joins itself 

 to the laryngeal branch of the superior thyroid 

 artery and runs along its upper edge, passes 

 between the lower margin of the os hyoides 

 and upper margin of the thyroid cartilage, and 

 reaches the upper edge of the larynx by per- 

 forating the thyro-hyoid ligament posterior to 

 the external edge of the thyro-hyoid muscle, 

 above the upper edge of the inferior constrictor 

 and below the lower edge of the middle con- 

 strictor of the pharynx, and a little in front of 

 the round ligament connecting the superior 

 cornu of the thyroid cartilage to the larger 

 cornu of the hyoid bone. Sometimes one or 

 two small twigs pass between the trunk of the 

 vagus and the superior laryngeal soon after the 

 origin of the latter, and the external branch 

 of the superior laryngeal occasionally comes 

 directly from the trunk of the vagus, a little 

 below the origin of the internal branch. While 

 the superior laryngeal nerve is passing behind 

 the internal carotid, it sends off several small 

 twigs, some of which communicate with the 

 phavyneeal plexus, a few pass downwards and 

 throw themselves into some of the cardiac 

 nerves, and the greater part run upon the sur- 

 face of the internal and external carotids, and 

 assist in forming, with the more numerous 

 branches from the sympathetic, the arterial 

 plexus of nerves winding round the carotid 

 arteries and their branches. 



External branch of the superior laryngeal. 

 It is strengthened by some twigs from the 

 superior ganglion of the sympathetic, passes 

 downwards and forwards over the inferior con- 

 strictor muscle of the pharynx and lateral 

 surface of the larynx, gets below the outer edge 

 of the sterno-thyroid, and continues its course 

 below it and the thyro-hyoid muscle. It gives 

 some twigs to the inferior constrictor muscle, 

 some filaments also to the upper part of the 

 sterno-hyoid and thyroid muscles, and to the 

 thyroid body. The continuation of the nerve 

 after sending a twig downwards to anastomose 

 with another twig from the inferior laryngeal 

 nerve behind the thyroid body, ultimately ter- 

 minates in the crico-thyroid muscle.f 



* The superior laryngeal nerve rarely passes in 

 front of the internal carotid. 



t A small twia; from the external branch of the 

 superior laryngeal perforates the thyroid cartilage 

 occasionally, and anastomoses with some of the 



Internal branch of the superior laryngeal. 

 As soon as this branch has perforated the thyro- 

 hyoid ligament and reached the outer surface 

 of the mucous membrane immediately beneath 

 it, it divides into numerous branches which 

 are flattened and radiating, some passing up- 

 wards and forwards towards the base of the 

 tongue and sides of the epiglottis, others for- 

 wards, downwards, and inwards in the aryteno- 

 epiglottidean folds to the surfaces of the epi- 

 glottis, and others downwards upon the posterior 

 surface of the larynx. The branches which 

 proceed forwards and upwards are small and 

 pass onwards to the glosso-epiglottidean folds ; 

 and while some of their filaments terminate in 

 these folds and in the mucous membrane at the 

 lateral and back part of the tongue, others turn 

 inwards and are distributed upon the sub- 

 mucous glands and the mucous covering of 

 the anterior and upper part of the epiglottis. 

 Several pretty strong branches pass forwards 

 and inwards in the aryteno-epiglottidean folds 

 to the side of the epiglottis. Some of these 

 proceed upon its anterior surface and are there 

 distributed upon the mucous membrane and 

 the submucous glands, sending also a few 

 filaments through small apertures in the epi- 

 glottis to be ramified in the mucous membrane 

 on its posterior or laryngeal surface; while 

 other branches pass upon the posterior aspect 

 of the epiglottis, some of them occupying 

 notches on its outer edge, and are distributed 

 upon the submucous glands and mucous mem- 

 brane covering that surface. A few branches 

 proceed downwards and forwards over the outer 

 surface of the lining mucous membrane of the 

 larynx, send some filaments to the laryngeal 

 sac, and may be traced as far as the inferior or 

 true vocal chords. A long slender branch 

 passes downwards on the outer surface of the 

 tlmo-arytenoid muscle, and between it and the 

 inner surface of the thyroid cartilage, and fre- 

 quently anastomoses with an ascending branch 

 of the recurrent or inferior laryngeal. One or 

 two slender filaments enter the thyro-arytenoid 

 muscle, and these, after a long and winding 

 course among the fibres of that muscle and 

 those of the crico-arytenoideus lateralis, ulti- 

 mately run to the mucous membrane of the 

 larynx. A pretty large branch runs backwards 

 in the posterior part of the thyro-arytenoid fold 

 of mucous membrane, transmitting at the same 

 time a few filaments downwards ; and on reach- 

 ing the arytenoid cartilage it sends several 

 filaments upon the posterior surface of the 

 proper arytenoid muscles, and continuing its 

 course downwards between the mucous mem- 

 brane of the pharynx and the crico-arytenoideus 

 posticus muscle, it anastomoses with one of the 

 posterior ascending branches of the recurrent. 

 The greater part of the filaments which enter 

 among the fibres of the arytenoideus posticus 

 and transversus muscles may be traced to the 

 mucous membrane of the larynx, and only a 

 very few appear to terminate among the mus- 

 cular fibres; others anastomose with arytenoid 



descending branches of the internal branch of the 

 same neive. 



