834 THE NERVES. 



upper wall of tne pharynx, below the guttural pouch. This plexus receives 

 a filament from the hypoglossal nerve. 



10. Tenth Paie, Vagus, or Pneumogastric Nerves (Figs. 452, 455, 



458, 480). 



The pneumogastric nerve is as remarkable for its extent, as for the multi- 

 plicity of physiological uses ascribed to it. 



It is prolonged beyond the stomach, after distributing to that viscus, the 

 oesophagus, pharynx, lung, bronchi, trachea, and larynx a large number of 

 filaments on which depend the movements, secretory functions, and purely 

 sensory phenomena of which all these organs are the seat. 



Origin. — The pneumogastric is a fixed nerve, and consequently arises from 

 two kinds of roots ; these we will successively describe before passing to its 

 distribution, though it must be remarked that this subject has not yet been fuhy 

 determined. 



Sensitive roots. — These arise from a nucleus of grey substance situated near 

 the floor of the fourth ventricle, a little behind the glosso-pharyngeal nucleus — 

 sensitive nucleus of the mixed nerves (Fig. 455, pn) — and in which the fibres of 

 the antero-lateral columns of the medulla oblongata, or respiratory tract of Bell, 

 appear to be lost. In leaving the medulla, they form from four to ten bundles, 

 which describe a shght curve with convexity upwards ; the highest middle fibres 

 coi-respond to the groove that limits, superiorly, the respiratory fasciculus, the 

 posterior and anterior fibres bending downwards to the pyramids — the second 

 more than the first. 



These roots proceed transversely outwards, mixed with connective tissue 

 and some fine muscular ramifications, and leave the cranium by one of the 

 openings (jugular foramen) in the posterior part of the foramen lacerum, 

 uniting in their passage through that aperture into a somewhat voluminous 

 ganglion, called in Man the jugular ganglion {iqiper ganglion, or ganglion of the 

 root). 



Motor roots. — Several anatomists and physiologists consider these as a portion 

 of the accessory nerve of Willis, and give them the name of internal or bulbar 

 root of the spinal nerve. They are situated a little behind the preceding, and 

 arise, in the middle of the respiratory tract, from a mass of grey substance which 

 also emits the motor fibres of the glosso-pharyngeal {motor nucleus of mixed nei'ves 

 — Fig. 455, s) ; consequently, they are not so elevated as the whole of the sensitive 

 fibres. They are separated from the latter by a comparatively large vein, and are 

 distinguished from them by their anastomotic tendency. Becoming longer as 

 they are more posterior, and frequently anastomosing with each other, the fila- 

 ments forming these motor roots converge, and gain the posterior part of the 

 foramen lacerum ; this they pass through by one or two special openings to join 

 the jugular ganglion, beneath and behind which we find them applied. A certain 

 number of the most posterior of these filaments lie beside the medullary root of 

 the spinal accessory nerve ; but they are soon detached to pass with the others to 

 the jugular ganglion. 



Jugidar or Ehrenritter's ganglion. — Elongated from before to behind, and 

 flattened above and below, the jugular ganglion is embedded in the cartilaginous 

 substance that fills the foramen lacerum. When it has been macerated for some 

 time in dilute nitric acid, it may be resolved into two portions — one correspond- 

 ing to the sensitive, the other to the motor roots. Some white nerve-filamentiS 



