The sympathetic system consists essentially of a chain of ganglia on
each side of the ventral surface of the vertebral column, interconnected
by longitudinal nerve-cords, and stretching from the base of the skull
to the tail. The ganglia are connected to the spinal nerves by
communicating branches, and numerous branches pass from them to the
abdominal and thoracic viscera, and to the walls of the lymph- and
blood-vessels, forming complicated plexuses.
=Cervical portion= (Fig. 156, page 379).--The sympathetic system begins
just caudad of the tympanic bulla as the =superior cervical ganglion=
(=G. cervicale superius=) (Fig. 156, _e_). This is a large ganglion
closely applied to the ganglion nodosum (_d_) of the vagus, and lying on
its ventrocranial side. From the superior cervical ganglion the
sympathetic trunk passes caudad usually closely bound up with the vagus
(_d′_), so that the two can scarcely be distinguished. They lie (_i_) at
the side of the trachea (6), close against the lateral surface of the
carotid artery. A few centimeters before reaching the first rib the two
separate (Fig. 157, page 381); the sympathetic (_c_) is here the smaller
and more dorsal of the two. Just craniad of the first rib the
sympathetic usually forms a small swelling, the =middle cervical
ganglion= (Fig. 157, _d_), beyond which it divides into two portions.
The larger dorsal division passes dorsocaudad and joins a large
ganglion, the =inferior cervical= (_e_), which lies at the head of the
first rib, on the lateral surface of the longus colli muscle. The
ventral branch (_g′_) passes caudad, turns laterad about the medial and
caudal surface of the subclavian artery, and likewise reaches the
inferior cervical ganglion.
In some cases the middle cervical ganglion (_d_) is lacking.
=Branches of the Sympathetic in the Cervical Region.=--From the cranial
end of the superior cervical ganglion several nerves pass craniad. Some
of these become connected immediately with the cranial nerves emerging
from the jugular foramen, forming a plexus in this region. Others pass
with the internal carotid artery craniad, forming a plexus about that
artery; from the plexus twigs arise which pass to the fifth and sixth
cranial nerves; doubtless also to the seventh and eighth. A specially
large branch, the =deep petrosal nerve= (see page 373), passes from the
superior cervical ganglion along with the internal carotid artery to the
pterygoid canal, thence through this to the =sphenopalatine= ganglion.
Before separating from the vagus the sympathetic gives off one or two
=cardiac= nerves (Fig. 157, _i_). These are closely bound up with the
vagus (_b_), so that they appear usually to have origin from the vagus
at about the level of the first rib. These pass with the vagus to the
heart and take part in the formation of the =cardiac plexus= (_k_).
At the middle cervical ganglion (_d_) usually a communicating branch is
given to the vagus. The branches of the inferior cervical ganglion (_e_)
fall in the thoracic region, and are described in that connection.
=Thoracic Portion of the Sympathetic= (Fig. 157, page 381).--The
inferior cervical ganglion (_e_) lies entirely within the thoracic
cavity. It has the following branches:
1. One or two small =cardiac= branches (_h_), which pass to the heart
(_r_).
2. A =large communicating branch= (_e′_), which passes craniad from the
cranial end of the ganglion (_e_) along the lateral surface of the
longus colli muscle, and gives communicating branches to the sixth,
seventh, and eighth cervical nerves (_VI_, _VII_, and _VIII_).
3. One or two small communicating branches to the first thoracic nerve
(_I′_).