To evaluate hypoglossal nerve function, a neurologist asks her patient to protrude his tongue. On
doing so, his tongue deviates to the right side. This finding results from paralysis of which of the
following muscles?
A. Left genioglossus
B. Left hyoglossus
C. Left palatoglossus
D. Right genioglossus
E. Right hyoglossus
F. Right palatoglossus
The correct answer is D. The genioglossus muscle is innervated by the hypoglossal nerve. The
function of the genioglossus muscle is to pull the tongue forward (protrude) and toward the
opposite side. When the right genioglossus muscle is paralyzed, the left genioglossus muscle
pulls the tongue forward and to the right.
If the left genioglossus muscle were paralyzed (choice A), the tongue would deviate toward the
left on protrusion because of the unopposed action of the right genioglossus muscle. The left
genioglossus muscle is innervated by the left hypoglossal nerve.
The hyoglossus muscles (choices B and E) are innervated by the hypoglossal nerves. The
function of these muscles is to retract the tongue. These muscles are not active during protrusion
of the tongue.
The palatoglossus muscles (choices C and F) are innervated by the vagus nerves, rather than the
hypoglossal nerves. Their function is to pull the tongue back (retract) and upward toward the
palate.