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THE NERVOUS SYSTEM. 277 ;
Compound Net-veH are those composed of motor and sensory filaments,
and in some instances combining motion, sensation, and special sense
example, the inferior maxillary or third divis-
Fig. 138.
ion of the fifth.
With the exception of the ninth, tenth, and
eleventh pairs, the cranial nerves are distrib-
uted to the liead alone ; those excepted have
also a distribution to the neck, the tenth pair
passing to the thorax and abdomen.
The regions supplied by the cranial nerves
are diagrammatically represented in Fig. 138,
from which it will be seen that nine of the
fourteen regions upon the head and neck are
supplied with sensation by some of the branches
of the fifth pair of nerves.

Olfactory Nerves.
The Nervous Distribution of the
Head (Kaiiney): 1, region sup-
The olfactory or first pair of nerves (Fig. 139) plied by the supraorbital branch
of the fifth nerve ; 2, supplied by
are those concerned in the special sen.se of smell.
the supratrochlear branch of the
They are about twenty in number, and derive fifth nerve ; 'A, supplied by the in-
fratrochlear branch of the fifth
their superficial origin from the under surface nerve; 4, supplied by the infra-
orbital branch of the fifth nerve;
of the olfactory bulb of the brain, m hich is sit- T). supplied by the buccal branch
of the fifth nerve fi, supplied by
uated on the under, proximal, and forward ;
the mental branch of the fifth
portion of the anterior lobe of the cerebrum. nerve; 7, supplied by the super-
ficial cervical from the cervical
These bulbs rest upon the olfactory sulcus of plexus ; 8, supplied by the great
auricular from the cervical plex-
the cribriform plate of the ethmoid bone, being us; 9, supplied by the temporo-
malar branch of the fifth nerve;
separated from each other by the crista galli.
10, supplied by the lachrymal
The nerves pass downward through the nu- branch of the fifth nerve; 11,
sujiplied by the auriciilo-tem-
merous foramina in the cribriform plate into poral branch of the fifth nerve;
12, supplied by the great occipi-
the superior nasal chamber. Th^y are invested tal (a spinal nerve) ; IH, supplied
by the small occipital from the
by a covering derived from the membranes of
cervical plexus ; 14, supplied by
the brain, and are distributed to the mucous the supraclavicular from the
cervical plexus.
lining of the superior meatus of the nose.
The nerves are divided into three sets—inner, outer, and middle. The
inner set is composed of the largest nerves : they are situated next to the
median line, and pass into delicate gi'ooves or canals which descend on
either side of the perpendicular plate of the ethmoid bone. Some of
these canals run obliquely forward, and others obliquely backward.
Those that arise from the lateral portions of the olfactory lobes pass
into fine canals, which subdivide as they penetrate the lateral masses
of the ethmoid. A few of the more central of these nerves are dis-
tributed to the roof of the nasal chamber. No filaments extend to the
vomer or inferior turbinated bones. The olfactory nerves differ from
all other cranial nerves in being composed of non-medullated fibres.
Their terminal branches communicate freely with each other and form
a plexus beneath the nasal mucous membrane.