982 THE NERVOUS SYSTEM 



The Motor Fibres arise from the nucleus ambiguus in the lateral column of the 

 medulla, in line with the motor nucleus of the facial nerve. From this nucleus they 

 pass at first dorsalwards and then, turning lateralwards, they emerge and join the 

 sensory fibres and run with them in the trunk of the nerve (fig. 598). 



Van Gehuchten's observations point to the conclusion that one motor nucleus of the ninth 

 nerve is separate from and lies above and to the medial side of the nucleus ambiguus, and that 

 a portion of the nucleus of the ala cinerea is also a motor nucleus common to the ninth and tenth 



Central Connections. The nuclei of termination of the ninth nerve are connected with the 

 motor nuclei of other cranial nerves by the medial longitudinal fasciculus, and with the som- 

 sesthetic area of the cortex cerebri by the medial lemniscus (fillet). The motor nucleus of the 

 ninth nerve is associated with the somacsthetic area by the pyramidal fibres. 



THE TENTH NERVE THE VAGUS OR PNEUMOGASTRIC 



The vagus or pneumogastric nerves are the longest of the cranial nerves, and they 

 are remarkable for their almost vertical course, their asymmetry, and their exten- 

 sive distribution, for, in addition to supplying the lung and stomach, as the name 

 'pneumo-gastric' indicates, each nerve gives branches to the external ear, the phar- 

 ynx, the larynx, the trachea, the oesophagus, the heart, and the abdominal viscera. 

 Each nerve is attached to the side of the medulla, in the postero-lateral sulcus, be- 

 hind the olivary body, by from twelve to fifteen root filaments which are in linear 

 series with the filaments of the glosso-pharyngeal nerve. The filaments pierce the 

 pia mater, from which they receive sheaths, and, traced outwards, they pass into the 

 posterior fossa of the cranium towards* the jugular foramen and unite to form the 

 trunk of the nerve, which passes through openings in the arachnoid and the dura 

 mater which are common to it and to the eleventh nerve. In the jugular foramen a 

 small spherical ganglion, the jugular ganglion, is interposed in the trunk of the nerve, 

 which here turns at right angles to its former course and descends through the neck. 

 As it leaves the jugular foramen it is joined by the internal or accessory portion of the 

 eleventh nerve, and immediately below this junction it enters a large ovoid ganglion, 

 the ganglion nodosum or ganglion of the trunk (fig. 707) . As it descends through the 

 neck the nerve passes ventral and somewhat lateral to the superior cervical sympa- 

 thetic ganglion, and in front of the longus capitis and longus colli, from which it is 

 separated by the prevertebral fascia. In the upper part of the neck it is placed be- 

 tween the internal carotid artery and the internal jugular vein, and on a plane dorsal 

 to them, the artery being ventral and mesial, and the vein ventral and lateral. In the 

 lower part of the neck it occupies a similar position in regard to the common carotid 

 artery and the internal jugular vein, and the three structures are enclosed in a com- 

 mon sheath derived from the deep cervical fascia, but within the sheath each struc- 

 ture occupies a separate compartment (fig. 707). In the root of the neck and in 

 the thorax the relations of the nerves of the two sides of the body differ somewhat, 

 and they must, therefore, be considered separately. 



The right vagus passes in front of the first part of the right subclavian artery 

 in the root of the neck and then descends in the thorax, passing obliquely down- 

 wards and backwards on the right of the trachea, and behind the right innominate 

 vein and the superior vena cava, to the back of the root of the right lung. Just 

 before it reaches the right bronchus it lies close to the inner side of the vena azygos 

 as the latter hooks forwards over the root of the lung. At the back of the right 

 bronchus the right vagus breaks up into a number of branches which anastomose 

 with the branches of the sympathetic to form the right posterior pulmonary plexus, 

 and from this plexus it issues in the form of one or more cords which descend on the 

 oesophagus and break up into branches which anastomose with branches of the left 

 vagus, forming the posterior resophageal plexus. At the lower part of the 

 thorax fibres of this plexus become again associated in one trunk which passes 

 through the diaphragm on the posterior surface of the oesophagus, and is distributed 

 to the posterior surface of the stomach and to the coeliac (solar) plexus and its offsets. 



The left vagus descends through the root of the neck between the carotid and 

 subclavian arteries and in front of the thoracic duct. In the upper part of the 

 superior mediastinum it is crossed in front by the left phrenic nerve, and in the lower 

 part of the same region it crosses in front of the root of the subclavian artery and 

 the arch of the aorta and behind the left superior intercostal vein. Below the aortic 



