. 5. Branches
to the lungs. 4. Branches to the
liver. 6. Branches to the stomach.]

THE CRANIAL NERVES. From the brain, nerves are given off in pairs, which
succeed one another from in front backwards to the number of twelve. The
_first_ pair, the _olfactory_ nerves, are the nerves of the sense of
smell. The _second_ pair are the _optic_, or the nerves of the sense of
sight. The _third_ pair are called the _motores oculi_, the movers of
the eye, from the fact that they are distributed to all the muscles of
the eye with the exception of two. The _fourth_ pair and the _sixth_
pair each supply one of the muscles of the eye, on each side, the fourth
extending to the superior oblique muscle, and the sixth to the external
rectus muscle. The nerves of the _fifth_ pair are very large; they are
each composed of two bundles of filaments, one motor and the other
sensory, and have, besides, an additional resemblance to a spinal nerve
by having a ganglion on each of their sensory roots, and, from the fact
that they have three chief divisions, are often called the _trigeminal_,
or _trifacial_, nerves. They are nerves of special sense, of sensation,
and of motion. They are the sensitive nerves which supply the cranium
and face, the motor nerves of the muscles of mastication, the
_buccinator_ and the _masseter_, and their third branches, often called
the _gustatory_, are distributed to the front portion of the tongue, and
are two of the nerves of the special sense of taste. The _seventh_ pair,
called also the _facial_ nerves, are the motor nerves of the muscles of
the face, and are also distributed to a few other muscles; the _eighth_
pair, termed the auditory nerves, are the nerves of the special sense of
hearing. As the _seventh_ and _eighth_ pairs of nerves emerge from the
cavity of the skull together, they are frequently classed by anatomists
as one, divided into the _facial_, or _portio dura_, as it is sometimes
called, and the _auditory_, or _portio mollis_. The _ninth_ pair, called
the _glosso-pharyngeal,_ are mixed nerves, supplying motor filaments to
the _pharyngeal muscles_ and filaments of the special sense of taste to
the back portion of the tongue. The _tenth_ pair, called the
_pneumogastric_, or _par vagum_, are very important nerves, and are
distributed to the larynx, the lungs, the heart, the stomach, and the
liver, as shown in Fig. 60. This pair and the next are the only cerebral
nerves which are distributed to parts o