Vascular and cardiac branches.—The vagus in its passage along the neck sends off directly from its trunk several filaments, which throw themselves into the arterial nervous plexuses sur rounding the carotid arteries and their branches; and also others which pass downwards and join themselves, either directly or indirectly, to the cardiac plexus. These branches are very variable in their number, size, and origin, so that it is impossible to give any description of them which will be found generally applicable, and they commonly cliff& on the two sides in the same individual.
Vascular branches (rami vasculares).- Several small branches arise from the trunk of the vagus between the origin of the superior laryngeal nerve, and about a line or so below the level of the bifurcation of the common carotid, and chiefly pass upon the carotid arteries and their branches. Valentin s has divided these into 1. Rami carotici, consisting of two or three larger and some smaller twigs, coming off from the vagus near the origin of the superior laryngeal and also from the commencement of the superior laryngeal. They run inwards and forwards upon the internal carotid.
2. Rams ad divisionem arteries carotidis is principally distributed upon the common carotid at its bifurcation.
3. Rami vasculares posteriores et interni are generally three in number, come from that part of the trunk of the vagus on a level with the bifurcation of the common carotid, and run principally, as their name implies, to the nervous plexus on the posterior and inner part of the large neighbouring arteries.
4. Rand vasculares anteriores et interni spring from the trunk of the vagus a very little below the origin of the last, run to the outer side of the common carotid, and assist with some of the other branches of the vagus and sympathetic in forming a nervous network on the outer and anterior side of this artery, while one or more twigs proceed downwards to join the superior cardiac nerve of the vagus.
Cardiac nerves.—Two or three cardiac bran ches come from the inner side of the vagus at some little distance from each other; the upper of these generally arises a little below the bifur cation of the common carotid. These bran ches proceed downwards and inwards, commu nicate freely with each other, send some filaments upon the surface of the common carotid artery, anastomose freely with the cardiac branches of the superior and middle cervical ganglia of the sympathetic and with the recurrent, pass chiefly in front of the large arteries at the root of the neck, and terminate in the upper part of the cardiac plexus of nerves. Frequently, more especially when the upper cardiac branches are small, or when some 'of them are want ing, we \find a pretty large cardiac branch arising froth-the_vagus about the upper part of the lower third of the neck, and passing down wards, on the right side in front of the subcla vian, on the left in front of the arch of the aorta, it throws itself into the upper part of the cardiac plexus. Two or more branches also leave the trunk of the vagus as it passes the subclavian on the right and the arch of the aorta on the left side, pass inwards and throw them selves partly into the cardiac plexus and partly into the anterior bronchial plexus.
Inferior laryngeal or recurrent branch.— ( Ramus laryngeus inferior seu recurrens.) On the right side the recurrent arises from the vagus as it is passing, over'the anterior surface of the subclavian artery, while on the left side it is sent off from the raps, generally from its inner side, as it is crossing the anterior surface of the transverse portion of the arch of the aorta. On the right side it hooks round the subclavian on the inner side of the scalenus anticus muscle, and passing upwards and inwards, first below the subclavian artery and then below the com mon carotid, it reaches the right side of the trachea. On the left side it hooks round the arch of the aorta and obliterated ductus arte riosus, and passing upwards and inwards below the aorta, the left subclavian at its origin, and the left common carotid, it reaches the left side of the trachea. The recurrent soon after its origin generally receives one or two additional twigs from the trunk of the vagus. Immedi
ately after it leaves the trunk of the vagus, it anastornoses freely with branches of the sympa thetic, chiefly with the internal branches of the two inferior cervical and first dorsal ganglia of the sympathetic,—and while the right send> some twigs upon the outer surface of the sub clavian artery, the left sends some upon the surface of the aorta. It also throws several twigs into the cardiac, tracheal, and bronchial plexuses. The left sends some twigs to the tracheal plexus, while the corresponding twigs of the right side come from the trunk of the vagus. The two recurrents then proceed up wards along the sides of the trachea towards the larynx,—the left resting upon the anterior surface of the cesophagus,—and are both co vered by the sterno-hyoid and sterno-thyroid muscles. In this part of the course of the re current it generally receives communicating twigs from tbe cardiac branches of the superior and middle cervical and sympathetic ganglia, and it also anastomoses with some of the upper cervical cardiac branches of the vagus. It also sends several twigs to the cesophagus and tra chea, ((esophageal and tracheal twigs of the recurrent,) some of which perforate the fibrous membrane between the cartilaginous rings of the trachea, and reach its mucous surface, while others are distributed among the muscular fibres which complete the cartilaginous rings behind. As it approaches the larynx it sends a twig upwards and forwards, which anastomoses with a descending twig of the external branch of the superior laryngeal ; and it gives some filarnents to the thyroid body, to the mucous membrane of the lower part of the pharynx, to the inferior constrictor of the pharynx, and also occasionally one or two slender filaments to the crico-thyroid muscle. It likewise sends a branch upwards Over the posterior surface of the larynx, first passing between the cesophagus and back part of the trachea, and then beneath the mucous membrane of the anterior part of the pharynx and crico-arytenoideus posticus muscle, sending some filaments to the cesophagus and mucous membrane of the pharynx, and anastomosing with the posterior descending twig of the inter nal branch of the superior laryngeal. The trunk of the recurrent now passes upwards in front of the lower edge of the inferior constrictor muscle, gets into the sulcus on the posterior surface of the articulation between the lower cornu of the thyroid cartilage and the external surface of the cricoid cartilage, and then passes along the outer edge of the crico-arytenoideus posticus upon the external surface of the crico arytenoideus lateralis and thyro-arytenoid mus cles, where it terminates. In its course along, the side of the larynx it generally sends a twig up wards to anastomose with one of the descending twigs of the internal branch of the superior laryngeal. As it is passing the crico-ary tenoideus posticus it sends some twigs into the external edge of that muscle, all of which enter among its fibres except one. This last twig, which does not enter among the fibres of the muscle, runs beneath its outer edge, and pro ceeding upwards and inwards between its an terior surface and the posterior surface of the cricoid cartilage, it reaches the lower edge of the arytenoideus obliquus and transversus, and is lost among their fibres. As the continuation of the recurrent passes over the surface of the cricoid-arytenoideuslateralis, it sends some fila ments inwards among the fibres of this muscle, and then proceeds upwards upon the thyro-aryte noid, into the interior of which it dips. Its ter minating filaments are distributed in the thyro arytenoid muscle, and a few only can be traced to the lining membrane of the larynx. We have thus seen, that while nearly all the filaments of the internal branch of the superior laryngeal, distributed to the larynx, ultimately run to its mucous surface, the greater part of the filaments of the recurrent are distributed in the muscles which are attached to and move the arytenoid cartilages.