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322 ANATOMY.

each other, and occasionally form a single trnnk. In this region the
two roots are contained in a single sheath of the (hira mater witii the
})nenmogastric nerve. A branch of connnunication extends between the
accessory and mednllarv j)ortions of the snperior ganglion of the pneu-
mogastric nerve.
The encranial portion of the spinal accessory is separated into two
divisions, internal and external, which are almost identical in origin
with the two roots of the main nerve.
The Interna/ ^lednllari/ or Acce^mry Portion, which contains nearly
all the fibres arising from the mednlla, passes over the inferior ganglion
of the pnenmogastric nerve (ganglion plexiformis), and becomes inti-
mately associated Avith it. It is distributed through the pnenmogastric
nerve to the larynx, pharynx, and other structures. (See Pnenmo-
gastric Nerv-e.)
The Exfernal or Spinal Portion (muscular brancli) is the longer of
the two branches, and contains nearly all the filaments which arise from
the spinal cord, and may receive all the fibres of the posterior root of
the first cervical nerve. It passes from the posterior lacerated foramen
downward, backward, and outward in front of the internal jugular vein,
but occasionally behind the vein, over the transverse process of the atlas,
to the superior third of the sterno-cleido-mastoid muscle. It generally
pierces this nuisi-le, th(jugh it may pass beneath it and appear in the pos-
terior cervical triangular s})ace beneath the trapezius muscle. It com-
municates by brandies with the medullary ])ortion in the posterior lace-
rated foramen, with the first cervical nerve, and the superior ganglion of
the pnenmogastric nerve, while beneath the trapezius muscle it gives off
branches Avhich unite with branches from the third, fourth, and fifth
cervical nerves which assist in forming the cervical ])lexus. It also
distributes branches to ])art of the sterno-cleido-mastoid muscle and
to the clavicular portion of the ti-ai)ezius muscle.

Hypoglossal Nerve.
The hy])oglossal, twelfth, or sublingual nerve (the ninth nerve accord-
ing to the arrangement of Willis) (Fig. 152) is the last of the cranial
nerves. Its chief function is in connection Avith the movements of the
tongue in deglutition and articulation. It is also distributed to all the
muscles which are attached to the hyoid bone. It arises superficially
or a])])ar('ntly by twelve or fourteen filaments, which ])ass from the
groove situated between the olivary body and the antei'ior pyramid of
the medulla oblongata. The filaments are collected into two separate
bundles, sujjcrior and inferior, which are directed outward, pass behind
the vertebral artery, and extend toward the anterior condyloid foramen;
and as they enter this foramen or foramina' they receive a separate
sheath from the dura mater, and imite into a single trunk as they
emerge from the brain-case and pass into the deep ]iortions of the neck.
From this point it extends to the median side of the internal jugular
vein and the pnenmogastric nerve, ft then descends the neck nearly
' Occasional Iv tliere are two foramina in tlie ocrij)ital l)oiie. When this is the case
the bnndles j)ass thron.ijh separate openings.