910 NEUROLOGY 



THE VAGUS NERVE (N. VAGUS; TENTH NERVE; PNEUMO GAS TRIG 

 NERVE) (Figs. 791, 792, 793). 



The vagus nerve is composed of both motor and sensory fibers, and has a more 

 extensive course and distribution than any of the other cranial nerves, since it 

 . passes through the neck and thorax to the abdomen. 



The vagus is attached by eight or ten filaments to the medulla oblongata in the 

 groove between the olive and the inferior peduncle, below the glossopharyngeal. 

 The sensory fibers arise from the cells of the jugular ganglion and ganglion nodosum 

 of the nerve, and, when traced into the medulla oblongata mostly end by arborizing 

 around the cells of the inferior part of a nucleus which lies beneath the ala cinerea 

 in the lower part of the rhomboid fossa. These are the sympathetic afferent fibers. 

 Some of the sensory fibers of the glossopharyngeal nerve have been seen to end in 

 the upper part of this nucleus. A few of the sensory fibers of the vagus, probably 

 taste fibers, descend in the fasciculus solitarius and end around its cells. The somatic 

 sensory fibers, few in number, from the posterior part of the external auditory 

 meatus and the back of the ear, probably join the spinal tract of the trigeminal as 

 it descends in the medulla. The somatic motor fibers arise from the cells of the 

 nucleus ambiguus, already referred to in connection with the motor root of the 

 glossopharyngeal nerve. 



The sympathetic efferent fibers, distributed probably as preganglionic fibers to 

 the thoracic and abdominal viscera, i. e., as motor fibers to the bronchial tree, 

 inhibitory fibers to the heart, motor fibers to the esophagus, stomach, small intes- 

 tine and gall passages, and as secretory fibers to the stomach and pancreas, arise 

 from the dorsal nucleus of the vagus. 



The filaments of the nerve unite, and form a flat cord, which passes beneath 

 the flocculus to the jugular foramen, through which it leaves the cranium. In 

 emerging through this opening, the vagus is accompanied by and contained in 

 the same sheath of dura mater with the accessory nerve, a septum separating 

 them from the glossopharyngeal which lies in front (Fig. 792). In this situation 

 the vagus presents a well-marked ganglionic enlargement, which is called the jugular 

 ganglion (ganglion of the root); to it the accessory nerve is connected by one or 

 two filaments. After its exit from the jugular foramen the vagus is joined by the 

 cranial portion of the accessory nerve, and enlarges into a second gangliform swell- 

 ing, called the ganglion nodosum (ganglion of the trunk} ; through this the fibers of the 

 cranial portion of the accessory pass without interruption, being principally 

 distributed to the pharyngeal and superior laryngeal branches of the vagus, but 

 some of its fibers descend in the trunk of the vagus, to be distributed with the 

 recurrent nerve and probably also with the cardiac nerves. 



The vagus nerve passes vertically down the neck within the carotid sheath, 

 lying between the internal jugular vein and internal carotid artery as far as the 

 upper border of the thyroid cartilage, and then between the same vein and the 

 common carotid artery to the root of the neck. The further course of the nerve 

 differs on the two sides of the body. 



On the right side, the nerve passes across the subclavian artery between it and 

 the right innominate vein, and descends by the side of the trachea to the back of 

 the root of the lung, where it spreads out in the posterior pulmonary plexus. From 

 the lower part of this plexus two cords descend on the esophagus, and divide to 

 form, with branches from the opposite nerve, the esophageal plexus. Below, these 

 branches are collected into a single cord, which runs along the back of the esophagus 

 enters the abdomen, and is distributed to the postero-inferior surface of the stomach, 

 joining the left side of the celiac plexus, and sending filaments to the lienal plexus. 



On the left side, the vagus enters the thorax between the left carotid and sub- 

 clavian arteries, behind the left innominate vein. It crosses the left side of the 



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