inferior parts of the body, at the sides and in front of the spinal
column, and is termed, collectively, the system of the _great
sympathetic_. These ganglia are intimately connected by nervous
filaments, and communicate with the cerebro-spinal system by means of
the motor and sensory filaments which penetrate the sympathetic. The
nerves of this system are distributed to those organs over which
conscious volition has no direct control.

[Illustration: Fig. 61.
Course and distribution of the great Sympathetic Nerve]

Four of the sympathetic centers, situated in the front and lower
portions of the head, are designated as the _ophthalmic,
spheno-palatine, submaxillary_ and _otic ganglia_. The first of these,
as its name indicates, is distributed to the eye, penetrates the
_sclerotic membrane_ (the white, opaque portion of the eyeball, with its
transparent covering), and influences the contraction and dilation of
the iris. The second division is situated in the angle formed by the
sphenoid and maxillary bone, or just below the ear. It sends motor and
sensory filaments to the palate, and _velum palati_. Its filaments
penetrate the carotid plexus, are joined by others from the motor roots
of the facial nerve and the sensory fibres of the superior maxillary.
The third division is located on the submaxillary gland. Its filaments
are distributed to the sides of the tongue, the sublingual, and
submaxillary glands. The otic ganglion is placed below the base of the
skull, and also connects with the _carotid plexus_. Its filaments of
distribution supply the internal muscles of the _malleus_, the largest
bones of the _tympanum_, the membranous linings of the tympanum and the
_eustachian tube._ Three ganglia, usually designated as the _superior,
middle_, and _inferior_, connect with the cervical and spinal nerves.