The Tongue Master:
• Motor only (GSE); Origin: Medulla; Exit: Hypoglossal Canal (often double/triple in ox)
• Target: All intrinsic and extrinsic tongue muscles (Styloglossus, Hyoglossus, Genioglossus)
• Function: Prehension (wrapping tongue around grass), deglutition (swallowing), lapping
• Clinical: Paralysis leads to tongue atrophy, 'lolling' (hanging out), inability to prehend food
• Listeria Connection: CN XII deficits (tongue paralysis) + CN V (dropped jaw) + CN VII (facial droop) = classic Listeriosis presentation

Cranial Nerve XII: The Hypoglossal Nerve

The final cranial nerve is purely motor, governing the complex muscular hydrostat that is the tongue—essential for prehension, manipulation of food, and deglutition.

Anatomical Topography

Origin: Medulla oblongata (hypoglossal nucleus).
Exit: Hypoglossal Canal—frequently double or triple in the ox (a variation rare in the horse).
Target Muscles:

• Extrinsic: Styloglossus (retraction/elevation), Hyoglossus (depression), Genioglossus (protrusion).
• Intrinsic: Longitudinal, transverse, and vertical muscles that shape the tongue for grasping.

Functional Significance

In cattle, the tongue performs the critical prehension function—wrapping around grass stems and tearing them against the dental pad. This requires coordinated contraction of all hypoglossal-innervated muscles. During swallowing, the tongue acts as a piston to propel the bolus into the pharynx.

Clinical Manifestations

Unilateral Paralysis: Tongue deviates toward the affected side when protruded (due to unopposed contralateral genioglossus action).

Bilateral Paralysis: Tongue hangs out of mouth ('lolling'), becomes flaccid, shows rapid atrophy, and accumulates food (sialosis). Animal cannot prehend or swallow effectively, leading to starvation and aspiration pneumonia.

Neurological Integration

Hypoglossal function is often tested alongside other cranial nerves in neurological exams. The combination of:

• CN XII deficit (tongue paralysis)
• CN V deficit (dropped jaw)
• CN VII deficit (facial paralysis)

...strongly suggests Listeria monocytogenes infection (circling disease), where bacteria ascend sensory branches of CN V and cause microabscesses in the brainstem affecting multiple cranial nerve nuclei.