sew Ft 
ie 
t 
< 
to the mylohyoid and anterior belly of the digastric muscles. (2) The mental 
branch of the inferior dental nerve is a trunk of considerable size arising from the 
main nerve in the imferior dental canal. It emerges from the lower jaw through 
the mental foramen, and is distributed by many ‘branches to the chin and lower 
lip. It communicates beneath the facial muscles with the supra-mandibular 
branches of the facial nerve (Fig. 458, p. 657). (8) The incisor branch is the terminal 
part of the inferior dental nerve remaining after the origin of the mental branch. 
It supplies the incisor and canine teeth. 
The otic ganglion (g. oticum) 1s situated beneath the inferior maxillary nerve 
just below the foramen ovale. Like the other gangha described above, it possesses 
three roots :—(1) A motor root, derived from the nerve to the internal pterygoid 
muscle ; (2) a sensory root, formed by the small superficial petrosal nerve trom the 
tympanic plexus (through which communications are effected with the tympanic 
branch of the glosso-pharyngeal nerve, and a branch from the geniculate ganglion 
of the facial nerve); (3) a sympathetic root, from the plexus on the middle 
meningeal artery (Fig. 462). 
Five branches arise from the ganglion—three communicating and two motor 
branches. The three communicating nerves are fine branches which join respectively 
the vidian nerve, the roots of the auriculo-temporal, and the chorda tympani 
nerve. The two motor nerves supply the tensor tympani and tensor palati 
muscles. 
644 THE NERVOUS SYSTEM. 
Summary.—The trigeminal, the largest and most complex of the cranial nerves, is (1) the 
chief sensory nerve for the face, the anterior half of the scalp, the orbit and eyeball, the nose ae 
nasal cavity, the lips, teeth, mouth, and two-thirds of the tongue; (2) the motor fibres of the 
nerve supply the muscles of mastication, the mylohyoid and anterior belly of the digastric, 
possibly the levator palati and azygos uvulie (through Meckel’s ganglion), and the tensor tympani 
and tensor palati muscles (through the otic ganglion); (3) through the gangha placed on the 
three divisions of the nerve, not only are important organs, areas, and muscles innervated, but 
communications are also effected with the sympathetic system, with the third nerve (lenticular 
ganglion), facial nerve (spheno-palatine and otic ganglia), and glosso-pharyngeal nerve (otic 
ganglion). 
In its distribution to the skin of the face the branches of the fifth nerve present two striking 
peculiarities :—(1) While the branches to the skin reach the surface at many poimts and in 
diverse ways, the three main divisions are severally, by their branches, responsible for the supply 
of three clearly demarcated cutaneous areas. (2) By numerous communications with the facial 
nerve, sensory fibres are given to the muscles of expression supplied by the facial nerve. 
THE SIXTH OR ABDUCENT NERVE 
The abducent nerve (n. abducens) issues from the brain at the lower border of 
the pons Varolii, just above the pyramid of the medulla oblongata (for deep origin, 
see p. 484). It is directed forwards, and pierces the dura mater of the posterior 
fossa of the base of the skull alongside the dorsum sell (Fig. 457, p. 636). It 
then occupies the imner wall of the cavernous sinus, and is placed on the outer 
side of the internal carotid artery. It passes through the sphenoidal fissure below 
the third and nasal nerves and between the two heads of the external rectus 
muscle (Fig. 455, p. 635). In the cavity of the orbit it supplies the external 
rectus muscle on its Inner (ocular) surface. 
Communications.—In the wall of the cavernous sinus the sixth nerve receives two 
communicating filaments :—(1) From the carotid plexus of the sympathetic, and (2) from 
the ophthalmic division of the trigeminal nerve. 
THE SEVENTH OR FACIAL NERVE 
The facial nerve (n. facialis) emerges from the brain at the posterior border of 
the pons Varolii, below the trigeminal nerve and internal to the auditory nerve (for 
deep origin, see p. 482). Between it and the latter nerve is the minute pars intermedia 
of Wrisberg (Fig. 452, p. 633). The nerve passes outwards through the internal 
auditory meatus, courses through the aqueduct of Fallopius in the petrous portion 
of the temporal bone, emerges in the base of the skull by the stylo-mastoid foramen, 
and passes forwards through the parotid gland to supply the museles of the face. 
In the internal auditory meatus the nerve is placed upon the auditory nerve, the 
. 
