Page 314 - My FlipBook

324 ANA TOMY.

the vessel, or upon its outer surface, to a point just above the tendon of
the omo-hyoid muscle. In its descent it distributes a small branch to
the anterior belly of this muscle. It then divides into two or three
branches, and receives one or two communicating branches from the
second and third cervical nerves (communicans noni). By this union a
plexiforni loop is formed, with its concavity upward. This loop occa-
sionally receives another small branch from the cervical nerves. From
this plexiforni loop branches are distributed to the sterno-hvoid, sterno-
thyroid, and omo-hyoid muscles, and sometimes to the cardiac and phrenic
nerves within the thorax.
The Thyro-hijoid Branch arises from the hypoglossal nerve in front
of the external carotid artery, from which point it descends, and is dis-
tributed to the thyro-hyoid muscle.
The Branches to the Tone/iie are the stylo-glossus, hyo-glossus, and
genio-glossus, wlii(;h are given off from the hypoglossal nerve while it
is located l)etween the mylo-hyoid and the hyo-glossus muscles. They
are distributed to the muscles indicated by their names, and send
branches to other muscles in the substance of the tongue, as well as to
the genio-hyoid muscle.
Variations.—Occasionally the right and left hypoglossal nerves com-
nnniicate by a branch wliich passes between them in the neighborhood
of the genio-hyoid muscle. In rare cases filaments are distributed to
the mylo-hyoid muscle (Krause). According to Luschka, E. Bischoif,
Holl, and others, the descendens noni nerve does not in reality arise
from the hypoglossal nerve, but is derived i*rom the upper cervical
nerves, which are tem])orarily associated with the hypoglossal. Holl
states that the branches going to the thyro-hyoid and genio-hyoid
muscles are composed of fibres which arise from the spinal nerves.