Page 395 - Clinical Anatomy

ECA6 7/18/06 6:54 PM Page 380

380 The central nervous system

From the nucleus ambiguus (Fig. 242) efferent fibres pass to the striped
muscles of the pharynx and larynx.

Distribution
The nerve is connected to the side of the medulla by about ten filaments
which lie in series with the glossopharyngeal nerve along the groove
between the olive and the inferior cerebellar peduncle. These filaments
unite to form a single bundle which passes beneath the cerebellum to the
jugular foramen. Two sensory ganglia are associated with this part of the
nerve: a superior, within the jugular foramen, and an inferior, immediately
beneath the skull.
The vagus then passes vertically downwards to the root of the neck,
lying in the posterior part of the carotid sheath between the internal jugular
vein and the internal and then common carotid arteries (Fig. 213). There are
a number of important branches in the neck: pharyngeal to the pharyngeal
and palatal musculature by way of the pharyngeal plexus; superior laryn-
geal, supplying the interior of the larynx above the vocal folds and the
cricothyroid and inferior constrictor muscles; and the superior and inferior
cardiac branches which are inhibitory to the heart.
Below the level of the subclavian arteries the course and relations of the
nerve on the two sides differ.
On the right side the recurrent laryngeal branch is given off as it crosses
the subclavian artery; beyond this the nerve descends through the supe-
rior mediastinum in close association with the great veins. Behind the
root of the lung it takes part in the formation of the pulmonary plexusand then
passes on to the oesophagus to form, with its fellow, the oesophageal plexus.
The left vagus enters the thorax in close association with the great arter-
ies, lying at first lateral to the common carotid and then crossing the arch of
the aorta (Fig. 38). The left recurrent laryngeal branch, which is given off as the
vagus crosses the aortic arch, passes below the ligamentum arteriosum,
behind the arch and then ascends in the groove between the trachea and the
oesophagus (Fig. 34a). The vagus then passes behind the root of the lung,
enters into the formation of the pulmonary plexus and passes on to the
oesophagus to form a plexus from which emerge two trunks, each compris-
ing fibres from both the left and right vagus.
The two vagi then enter the abdomen through the oesophageal opening
in the diaphragm, the anterior vagus passing on to the anterior surface and
the posterior passing to the posterior aspect of the stomach (Fig. 55).
Beyond this it is difficult to trace the course of the nerves, but branches are
given to the coeliac, hepatic and renal plexuses and, by way of these plexuses,
are distributed to the fore- and midgut and to the kidneys.

Clinical features

1◊◊Isolated lesions of the vagus nerve are uncommon but it may be
involved in injuries or disease of related structures.