Passage if the yaps along the neck to the origin if the iryerior or recurrent laryngeal branch —After the vagus emerges from the in ferior aperture of the foramen lacerum poste rius, it lies between the internal carotid artery and the internal jugular vein, the artery being internal and anterior, and at first separated a small distance from it, the vein being immedi ately posterior and external. The glosso-plia ryngeal is still placed on its anterior side, but soon leaves it and crosses the anterior surface of the internal carotid artery on its way to the root of the tongue. The spinal accessory is still on its posterior side, but a little above the transverse process of the atlas the external branch begins to diverge backwards and out wards, and passes beneath the upper part of the internal jugular vein to reach the inner sur face of the upper part of the sterno-cleido mastoid muscle. The sympathetic nerve lies immediately posterior to it. The hypoglossal approximates its outer edge immediately below the foramen lacerum, gradually gets upon its anterior surface, is seen emerging from the angle left between it and the external branch of the accessory, where these nerves begin to sepa rate, and opposite the transverse process of the atlas, or sometimes a little below this, it has crossed over its anterior edge, and proceeds forwards and inwards to reach the tongue. The hypoglossal, in crossing over the anterior sur face of the vagus, is very closely bound to it by cellular tissue, and some small communicating branches pass between them. Some small communicating bi-ariches also pass between this portion of the vagus and the external branch of the spinal accessory, the superior ganglion of the sympathetic, the glosso-pharyngeal, and the nervous loop formed by the anterior branches of the first and second cervical nerves in front of the tmnsverse process of the atlas. The vagus also in this part of its course generally sends a branch to join the descendens noni, and more rarely the descendens noni is almost entirely or altogether formed by this branch of the vagus.* All these nerves and bloodvessels in the upper part of the neck are surrounded and connected together by cellular devoid of adipose tissue. The vagus, after joining itself to the internal carotid artery, accompanies it to the point of bifurcation of the common carotid, and then continues its course down the neck, .enclosed in the same sheath with the common carotid and internal jugular vein, the artery being internal, and the vein external and also anterior. The nerve maintains the same rela tion to these two vessels on both sides as far as the lower part of the neck, where on the right side the artery and vein diverge from each other, the artery passing inwards and the vein outwards, to join itself to the vena innominata ; while on the left side the vein and artery have scarcely separated from each other, when the junctinn between the former and left suhclavian vein takes place. On the right side the nerve is seen lying in the interval between the inter nal jugular and the internal carotid, and while crossing the anterior surface of the right sub clavian artery nearly at rig,lit angles, it sends off the right inferior laryngeal or recurrent nerve. On the left side it passes downwards into the thorax, still lying close to the outer side of the left com mon carotid ; but as it proceeds onwards, it crosses obliquely the left subclavian artery near its origin, and passing over the transverse portion of the arch of the aorta, it there gives off the left inferior laryngeal nerve. On both sides it passes into the thorax beneath the vena innominata._ The vagus, on emerging from the foramen lacerum, is near to the outer edge of the rectus capitis anticus minor muscle ind in front of the rectus capitis lateralis ; in its pas sage down the neck it first crosses the anterior surface of the lateral part of the atlas, then proceeds along the anterior surface of the rectus capitis anticus major muscle, and lastly it de scends upon the longus colli. In the upper part of its course it lies deep, and crosses be neath the styloid process of the tempoml hone and stylo-pharyngeus muscle. In the middle oldie neck the two vagi nerves have approached nearer to each other, and are much more su perficial. In the lower part of the neck they are again placed deeper, and are covered by the stemo-hyoid, sterno-thyroid, and sterno cleido-mastoid muscles.
As the vagus emerges from the lower part „of the foramen lacerum, its fibres are arranged somewhat loosely together, and are not enclosed in any dense and compact neuri lema, so that it is larger here than at the lower part of the neck ; and when the cellular tissue surrounding it is removed, the outline of the superficial fibres can be readily tmced. About half an inch below the lower edge of the superior ganglion it enlarges still more, forming an oblong rounded swelling, from nine lines to an inch in length, and extending from about the transverse process of the atlas to midway between the transverse processes of the second and third cervical vertebrm (plexus gan glilbrmis nervi vagi, ganglion sccundum n.v.
of Wutzer, ganglion trunci n. v. of Benda, ganglion in ferius n. v. ) In the human species, though this swelling has a greyish colour, yet its appearance is that of a plexus more than of a true ganglion ; and Valentin states° that he has not yet obtained satisfactory evidence that it contains the ganglionic nucleated globules without the presence of which there can be no true ganglion, and he believes that the greyish appearance of this swelling depends upon fat globules placed in the intervals of the plexus. At the lower part of this gangliform enlarge ment the nerve becomes smaller, rounder, firmer, and of a whiter colour.* This inferior or second ganglion of the vagus has been long known. Fallopiust speaks of an oblong olivary svvelling on the vagus soon after its exit from the cmnium. Willis / has described it in the following words : "nervi truncus, ibidem major factus, in tumorem quemdam corpori calloso, seu ganglio similem, attolli atque excrescere videtur," and in fig. ix. he has delineated it under the .name of " plexus gangliformis paris vagi." Vieussens§ also describes and figures it, and terms it " plexus gangliformis cervica lis nervi octavi paris." Winslowll describes it as " une espece de ganglion." ' It has also been described by Prochaska,li' Wutzer, Scarpa, Bellingeri, &c. Some have considered it to be a true ganglion, others only a plexus. Some re strict the term of inferior ganglion to that por tion of the enlargement of the nerve immediately below the orig,in of the superior laryngeal nerve, and have described it as being placed upon the internal fibres only, so that, according to this view, some of the external fibres of the vagus and the strengthening fibres of the spinal ac cessory do not pass through it.
The vagus in its passage down the neck gives off pharyngeal, laryngeal, esophageal, cardiac, and vascular branches.
Superior pharyngeal branch (ramus pharyn geus seu prinzus n. v.)—This is by much the largest and most important pharyngeal bmnch of the vagus, and is frequently designated, par excellence, the pharyngeal branch of the vagus. It arises from the anterior surface of the vagus shortly after its exit from the foramen lacerum, and opposite the upper part of the atlas, and is evidently formed by fibres, partly from the internal branch of the accessory, and partly from the vagus. Generally the greater part of its filaments, occasionally nearly the whole, appear to come from the accessory. It passes inwards and a little downwards across the anterior sur face of the internal carotid artery, to which it is genemlly pretty closely connected by cellular tissue, and lies a little inferior to the glosso pharyngea lnerve.** Immediately after crossing the internal carotid, it passes over the ascend ing pharyngeal artery, and after a short course it reaches the surface of the middle constrictor muscle of the pharynx. As it is crossing the carotid it is-generally joined by one, two, or three small branches descending from the gloss°. pharyngeal, and at the point of their junction a small plexus or ganglion is formed on the pharyngeal. (Vide article GLosso-Paaavri GEAL NERVE.) At this point the pharyngeal generally divides into several branches.* Two of these are considerably larger than the others, and one of them passes inwards and upwards,, and the other inwards and downwards over the lateral surfa.ce of the pharynx; while the smaller branches, two or more in number, pass upon the surface of the internal carotid and neigh bouring bloodvessels, especially the arteria pharyngea ascendens, to assist in forming the nervous plexuses iurrounding them. The two larger branches which pass upon the surface of the pharynx are soon joined by branches from the superior ganglion of the sympathetic. The upper branch passes over the superior pharyn geal constrictor to its upper edge, sending filaments to that muscle, to the elevator palati, the palato-_pharyngeus, the azygos uvulre, and also to the stylo-pharyngeus, and anasto moses freely with the pharyngeal and tonsillitic branches of the glosso-pharyngeal nerve and twigs of the sympathetic coming from its superior cervical ganglion. The lower runs downwards over the surface of the middle and inferior constrictors, distributes twigs to these muscles, and anastomoses with the izferior pharyngeal branch of the vagus, the pharyngeal branches of the superior laryngeal, and with some filaments of the sympathetic.