The Great Sensory Divider:
• Largest cranial nerve; arises from Pons; splits into three divisions at trigeminal ganglion
• V1 (Ophthalmic): Sensory only; exits Foramen Orbitorotundum (ox); supplies cornea, forehead, nasal cavity, goat horn (partial)
• V2 (Maxillary): Sensory only; gives rise to Cornual nerve (bovine horn); runs with Maxillary Artery
• V3 (Mandibular): Mixed; exits Foramen Ovale (ox); motor to muscles of mastication (Masseter, Temporalis, Pterygoids)
• Clinical: V3 lesion = "Dropped jaw" + inability to chew; jaw deviates toward lesion side
• Angiology: Rete Mirabile Epidurale surrounds trigeminal ganglion (infection risk)

The Great Sensory Nerve of the Head

The Trigeminal is the largest cranial nerve, serving as the architect of sensation for the face and the motor engine for chewing. It arises from the Pons and splits into three divisions at the Trigeminal Ganglion.

Angiology Correlation: The Rete Mirabile

In the bovine, the internal carotid artery regresses during development. The brain is supplied by the Rete Mirabile Epidurale, a meshwork of arteries derived from the maxillary and vertebral arteries. The Trigeminal Ganglion lies in close proximity to the cavernous sinus and this arterial rete. Infection in the cavernous sinus (from severe sinusitis or horn base infections) can easily compromise the Trigeminal nerve.

Division 1: Ophthalmic Nerve (V1) - Purely Sensory

Course (Ox): Travels in the cavernous sinus and exits via the Foramen Orbitorotundum.

Branches:

• Frontal Nerve: Emerges from orbit to supply upper eyelid and forehead skin. In the Ox, exits orbit directly (supraorbital foramen transmits vessels primarily).
• Lacrimal Nerve: Sensory to lacrimal gland and lateral canthus.
• Nasociliary Nerve: Parent trunk for ethmoidal and infratrochlear nerves.
  • Infratrochlear Nerve: Runs along medial orbital wall; supplies medial canthus, lacrimal sac, third eyelid.
  • Critical Variant (Goat): The Infratrochlear sends a cornual branch to the horn bud. This is the "Goat Trap"—blocking only the Cornual nerve (V2) fails to anesthetize the goat horn.

Division 2: Maxillary Nerve (V2) - Purely Sensory

Course (Ox): Exits via Foramen Orbitorotundum; enters Pterygopalatine Fossa; runs alongside Maxillary Artery.

Major Branches:

• Zygomatic Nerve: Divides into zygomaticofacial (cheek) and zygomaticotemporal.
  • Cornual Nerve: Branch of zygomaticotemporal; THE specific sensory nerve to the bovine horn. Ascends along temporal ridge.
• Infraorbital Nerve: Continuation of maxillary nerve; travels through Infraorbital Canal.
  • Dental supply: Superior Alveolar nerves to upper premolars/molars within canal.
  • Exit: Infraorbital Foramen.
  • Terminal branches: Supply muzzle, upper lip, nostrils (Nasolabial nerve).
• Pterygopalatine Nerve: Supplies hard and soft palate (Major and Minor Palatine nerves).

Division 3: Mandibular Nerve (V3) - Mixed

Course (Ox): Exits via discrete Foramen Ovale (unlike horse where it uses Foramen Lacerum).

Motor Branches:

• Muscles of Mastication: Masseter (power closure), Temporalis (closure), Pterygoids (lateral grinding), Mylohyoid, Digastricus (anterior belly only—opens jaw).

Sensory Branches:

• Buccal Nerve: Sensory to cheek mucosa (NOT the buccinator muscle—that's CN VII).
• Auriculotemporal Nerve: Sensation to ear and temporal region.
• Lingual Nerve: Sensation (touch/pain/temp) to rostral 2/3 of tongue.
• Inferior Alveolar Nerve: Enters Mandibular Foramen on medial ramus; supplies all lower teeth; exits Mental Foramen as Mental Nerve (lower lip/chin).

Clinical Signs of V3 Damage

"Dropped jaw" with inability to chew. The tongue may hang out. In unilateral lesions, the jaw deviates toward the side of the lesion due to unopposed action of healthy contralateral pterygoid muscles pushing the jaw across.