Neuroanatomy Draw It To Know It

12. Cranial Nerves 3, 4, 6, 12 197

Cranial Nerve 12

■ Th e hypoglossal nucleus spans most of the height of
the medulla.
■ Cranial nerve 12 exits the medulla between the
medullary pyramid and the inferior olive, passes
through the premedullary cistern, and exits the skull
base through the hypoglossal canal; then, it passes
through the medial nasopharyngeal carotid space and
terminates in the tongue musculature.
■ Th e hypoglossal nerve innervates the large intrinsic
tongue muscle mass, and it innervates three of the

four extrinsic tongue muscles: styloglossus,

hyoglossus, and genioglossus.

■ Palatoglossus is the only extrinsic tongue muscle not

innervated by cranial nerve 12; its innervation comes

from cranial nerve 10, the vagus nerve.

■ When one side of the genioglossus is denervated, the

tongue moves forward and toward the weakened side

(away from the intact side).

Inferior rectus m.

Lateral rectus m.

Inferior oblique m.

Tendinous ring

(opened)

Superior

orbital fissure

Sphenoid bone

Clivus

IV

III

VI

Cavernous

sinus

Internal carotid a.

Medial rectus m.

Superior rectus m.

Levator palpebrae m.

Superior oblique m.

FIGURE 12-1 Sagittal view of cranial nerves 3, 4, and 6. Used with permission from Baehr, Mathias, M. Frotscher, and Peter Duus. Duus’ Topical
Diagnosis in Neurology: Anatomy, Physiology, Signs, Symptoms, 4th completely rev. ed. Stuttgart; New York: Th ieme, 2005.