VAN 121: Veterinary Gross Anatomy-II (2+2)

Facial nerve

FACIAL NERVE (MIXED)

• This is the seventh cranial nerve and is a mixed nerve. It arises from the lateral part of the corpus trapezoideum immediately behind the pons.
• It passes outwards across the fifth cranial nerve and in front of the eighth cranial nerve and enters the internal auditory meatus with it. At the bottom of this meatus the two nerves get separated and the facial nerve enters the facial canal passes in it at first, directed outward, then curves backward and ventrally into the posterior wall of the tympanum to end at the stylo mastoid foramen.
• The bent part of the nerve is the genu and bears at its highest point the geniculate ganglion. After its emergence through the stylo mastoid foramen, the nerve passes forward and outward under the parotid salivary gland where it terminates into dorsal and ventral buccal nerves.

• The following branches are detached within the facial canal.
  • Great superficial Petrosal nerve: It arises from the geniculate ganglion in the facial canal, passes backward, reaches the cranial cavity through the internal auditory meatus, emerges through the foramen lacerum and is continued as the nerve of pterygoid canal to sphenopalatine ganglion. This nerve conveys parasympathetic (preganglionic) fibres to the lacrimal gland and glands of nasal mucosa that after relay in the spheno palatine ganglion, are conveyed to these structures in the respective branches of the trigeminal nerve.
  • Stapedial nerve: It is detached as it turns in the facial canal. It supplies stapedius muscle in the middle ear.
  • Chorda tympani nerve: It is given off a little below the preceding. It enters the tympanic cavity, passes across it and then descends and emerges through the petrotympanic fissure, gains the company of the lingual branch of the fifth nerve and supplies gustatory fibers to the anterior two third of the mucous membrane of the tongue. It also supplies secreto motor fibres to the submaxillary and sublingual salivary glands through the submandibular ganglion. After emergence through the stylomastoid foramen, the facial nerve gives off the following branches:
  • Posterior auricular nerve: Which runs upward and backward under the parotid gland and supplies posterior auricular muscles.
  • Internal or deep auricular nerve: Passes through a foramen in the conchal cartilage and supplies skin on the internal surface of the external ear.
  • Digastric branch: Descends below under the cover of parotid gland and supplies the posterior belly of digastricus, occipitohyoideus and stylohyoideus.
  • Auriculo palpebral nerve: Passes upward under the parotid gland and divides into anterior auricular branch supplying anterior auricular muscles and palpebral or temporal nerve which runs forward to supply orbicularis oculi, corrugator supercilli and levator nasolabialis.
  • A cervical branch that passes under parotid gland and parotidoauricularis muscle downward and backward and anastomoses with cutaneous branches of cervical spinal nerves.
  • Of the two terminal branches, the dorsal buccal nerve passes forward on the upper part of masseter and is joined by a branch from the superficial temporal division of the trigeminal nerve. It continues forward under zygomaticus and along the ventral border of dilator naris lateralis and ramifies on the muscles of the upper lip and nostril. It also supplies zygomaticus, malaris and buccinator. It anastomoses with ventral buccal nerve and receives a communicating branch along the anterior border of masseter.
  • The ventral buccal nerve passes downward obliquely across the lower part of masseter, runs forward along the ventral border of depressor labii inferioris. It supplies the muscles of the lower lip. ( View the Nerves supplying the face )