THE ABDUCENT NERVE—THE FACIAL NERVE 801 
downward and forward, lying at first between the ramus of the mandible and the 
medial pterygoid muscle, then on the medial face of the mylo-hyoid. On reaching 
the root of the tongue it divides into superficial and deep branches. The super- 
ficial branch (Ramus superficialis) runs forward on the stylo-glossus and accom- 
panies the mandibular duct on the deep face of the sublingual gland. It supplies 
the mucous membrane of the tongue and the floor of the mouth. At the root of the 
tongue it gives off a recurrent branch to the isthmus faucium, which communicates 
with the lingual branch of the glosso-pharyngeal nerve. The larger deep branch 
(Ramus profundus) turns around the lower edge of the stylo-glossus and hyo- 
glossus, passes upward and forward between the latter muscle and the genio- 
glossus, and continues forward on the latter to the tip of the tongue. At the turn 
it gives off one or more ascending branches which ramify on the deep face of the 
hyo-glossus. It gives branches to the mucous membrane and the fungiform papille 
of the tongue, and anastomoses with branches of the hypoglossal nerve and with 
the superficial branch. Minute ganglia occur on the finer branches of the lingual 
nerve. The chorda tympani branch of the facial joins the lingual nerve at the origin 
of the latter and is incorporated with it in its distribution to the tongue. 
THE ABDUCENT NERVE 
The abducent nerve (N. abducens) emerges from the brain behind the pons 
and just lateral to the pyramid (Fig. 629). It passes forward across the pons, 
pierces the dura mater, and accompanies the third and ophthalmic nerves, below 
which it emerges through the foramen orbitale. In the orbit it divides into two 
branches which innervate the rectus lateralis and the retractor muscle of the eye- 
ball. Within the cranium it receives filaments from the carotid plexus of the sym- 
pathetic. 
The fibers of the abducent nerve are axones of the large multipolar cells of the abducent 
nucleus which is situated beneath the eminentia teres of the floor of the fourth ventricle. The 
nucleus lies within the loop formed by the fibers of origin of the facial nerve. It is connected 
with (a) the anterior olive; (b) the oculomotor nucleus of the opposite side; (c) the motor area of 
the cerebral cortex by means of the pyramidal tract of the opposite side. 
THE FACIAL NERVE 
The facial nerve (N. facialis) has its superficial origin at the lateral part of the 
corpus trapezoideum, immediately behind the pons (Fig. 629). It passes outward 
in front of the eighth nerve and enters the internal acoustic meatus. At the bottom 
of the meatus the two nerves part company, the facial coursing in the facial canal 
of the petrous temporal bone. The canal and nerve are at first directed outward 
between the vestibule and the cochlea, then curve backward and ventrally in the 
posterior wall of the tympanum to end at the stylo-mastoid foramen. The bend 
formed by the nerve is called the knee (Geniculum n. facialis), and bears at its 
highest point the round geniculate ganglion (G. geniculi). 
The nerve consists of two parts, motor and sensory. The motor part constitutes the bulk 
of the nerve. Its deep origin is from the cells of the facial nucleus, which is situated in the medulla 
above the facial tubercle. On leaving the nucleus the root-fibers pass dorso-medially, incline for- 
ward close to the median plane, and then bend sharply downward to the point of emergence. The 
highest point of the bend is subjacent to the gray matter of the eminentia teres in the floor of the 
fourth ventricle, and the abducent nucleus lies in the coneavity of the curve. The small sensory 
part (N. intermedius) consists of axones of cells of the geniculate ganglion, which is interposed on 
the facial nerve as it bends downward in the facial canal. The fibers of this part, after entering 
the medulla, pass to the nucleus of termination which it shares with the ninth and tenth nerves. 
The peripheral fibers from the geniculate ganglion constitute the chorda tympani. 
After its emergence through the stylo-mastoid foramen (Fig. 646) the nerve 
passes ventrally, forward, and outward on the guttural pouch under cover of the 
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