PNEUMOGASTRIC, OR PAR VAGUM NERVE. 647 



The auricular nerves are sometimes described in connection with the facial. They 

 are given off from the ganglion of the trunk of the pneumogastric, and are composed of 

 filaments of communication from the facial and from the glosso-pharyngeal, as well as 

 of filaments from the pneumogastric itself. The nerves thus constituted are distributed to 

 the integument of the upper portion of the external auditory meatus, and a small filament 

 is sent to the membrana tympani. 



The pharyngeal nerves are very remarkable in their course. They are given off from 

 the superior portion of the ganglion of the trunk and contain a large number of the fila- 

 ments of communication which the pneumogastric receives from the spinal accessory. 

 In their course by the sides of the superior constrictor muscles of the pharynx, these 

 nerves anastomose with numerous filaments from the glosso-pharyngeal and the superior 

 cervical ganglion of the sympathetic, to form what is known as the pharyngeal plexus. 

 The ultimate filaments of distribution pass to the muscles and the mucous membrane of 

 the pharynx. Physiological experiments have shown that the motor influence transmitted 

 to the pharyngeal muscles through the pharyngeal branches of the pneumogastric is 

 derived from the spinal accessory. 



The superior laryngeal nerves are given off from the lower part of the ganglion of the 

 trunk. Their filaments come from the side opposite to the point of junction of the pneu- 

 mogastric with the communicating branch from the spinal accessory, so that probably 

 the superior laryngeals contain few if any motor fibres from this nerve. The superior 

 laryngeal gives off the external laryngeal, a long, delicate branch, which sends a few fila- 

 ments to the inferior constrictor of the pharynx and is distributed to the crico-thyroid 

 muscle and the mucous membrane of the ventricle of the larynx. The external laryngeal 

 anastomoses with the inferior laryngeal and with the sympathetic. The internal branch 

 is distributed to the mucous membrane of the epiglottis, the base of the tongue, the aryt- 

 eno-epiglottidean fold, and the mucous membrane of the larynx as far down as the true 

 vocal cords. A branch from this nerve, in its course to the larynx, penetrates the aryte- 

 noid muscle, to which it sends a few filaments, but these are all sensory. This branch 

 also supplies the crico-thyroid muscle. It anastomoses with the inferior laryngeal nerve. 

 An important branch, described by Cyon and Ludwig, in the rabbit, under the name of 

 the depressor-nerve, arises by two roots, one from the superior laryngeal and the other 

 from the trunk of the pneumogastric, passes down the neck by the side of the sympa- 

 thetic, and, in the chest, joins filaments from the thoracic sympathetic, to penetrate the 

 heart between the aorta and the pulmonary artery. This nerve will be referred to more 

 particularly in connection with the influence of the pneumogastrics upon the circulation. 



It is important, from a physiological point of view, to note that the superior laryngeal 

 nerve is the nerve of sensibility of the upper part of the larynx, as well as of the supra- 

 laryngeal mucous membranes, and that it animates a single muscle of the larynx (the 

 crico-thyroid) and the inferior constrictor of the pharynx. 



The inferior, or recurrent laryngeal nerves present some slight differences in their 

 anatomy upon the two sides. Upon the left side, the nerve is the larger and is given off 

 at the arch of the aorta. Passing beneath this vessel, it ascends in the groove between 

 the trachea and the oesophagus. In its upward course, it gives off certain filaments 

 which join the cardiac branches, filaments to the muscular tissue and mucous membrane 

 of the upper part of the oesophagus, filaments to the mucous membrane and the inter- 

 cartilaginous muscular tissue of the trachea, one or two filaments to the inferior con- 

 strictor of the pharynx, and a branch which joins the superior laryngeal. Its terminal 

 branches penetrate the larynx, behind the posterior articulation of the thyroid with the 

 cricoid cartilage, and are distributed to all of the intrinsic muscles of the larynx, except 

 the crico-thyroids, which are supplied by the superior laryngeal. Upon the right side, 

 the nerve winds from before backward around the subclavian artery, and it has essen- 

 tially the same course and distribution as upon the left side, except that it is smaller and 

 its filaments of distribution are not so numerous. 



