802 NERVOUS SYSTEM OF THE HORSE 



parotid gland, and passes between the origin of the superficial temporal and 

 internal maxillary arteries medially and the superficial temporal vein laterally. It 

 then crosses the posterior border of the ramus of the mandible ventral to the trans- 

 verse facial artery and about an inch and a half (ca. 3.5-4 cm.) below the articu- 

 lation of the jaw. Emerging from beneath the parotid gland upon the masseter 

 muscle, it receives the ventral branch of the superficial temporal nerve, and divides 

 into dorsal and ventral buccal branches. The following collateral branches are 

 given off, the first five being detached within the facial canal, and the others 

 between the stylo-mastoid foramen and the border of the jaw. 



1. The great superficial petrosal nerve (N. petrosus superficialis major) arises 

 from the geniculate ganglion. ^ It passes through the petrosal canal, contributing 

 a filament to the tympanic plexus, receives the deep petrosal nerve from the carotid 

 plexus of the sympathetic, emerges through the foramen lacerum, and is continued 

 as the nerve of the pterygoid canal to the sphenopalatine plexus and ganglia (Fig. 

 647). 



2. A delicate branch (R. anastomoticus cum plexu tympanico) emerges from 

 the geniculate ganglion and unites with a filament issuing from the tympanic plexus 

 to form the small superficial petrosal nerve (N. petrosus superficialis minor); this 

 ends in the otic ganglion. 



3. The stapedial nerve (N. stapedius) (Fig. 647) is a short filament detached 

 from the facial nerve as it turns down in the facial canal. It innervates the stape- 

 dius muscle. 



4. The chorda tympani (Fig. 647) is a small nerve which arises a little below the 

 preceding and pursues a recurrent course in a small canal in the mastoid part of 

 the temporal bone (Canaliculus chordae tympani), to reach the tympanic cavity. 

 It traverses the latter, passing between the handle of the malleus and the long branch 

 of the incus. Emerging through the petrotympanic fissure, the nerve passes down- 

 ward and forward on the guttural pouch, crosses beneath the internal maxillary 

 artery, and joins the lingual nerve. It sends twigs to the mandibular and sublingual 

 glands,, and through its incorporation with the lingual nerve furnishes fibers to the 

 mucous membrane of the anterior two-thirds of the tongue which are believed to 

 mediate the sense of taste. 



5. Anastomotic filaments unite with the auricular branch of the vagus near 

 the stylomastoid foramen. 



6. The posterior auricular nerve (N. auricularis aboralis) arises from the 

 facial at its emergence from the facial canal (Fig. 646). It runs upward and back- 

 ward with the posterior auricular artery under cover of the parotid gland, and sup- 

 plies the posterior and dorsal auricular muscles and the skin of the convex surface 

 of the external ear. It anastomoses with branches of the first and second cervical 

 nerves. 



7. The internal auricular nerve (N. auricularis internus) springs from the 

 facial close to or in common with the preceding (Fig. 646). It ascends in the 

 parotid gland just behind the styloid process of the conchal cartilage, passes 

 through an opening in the cartilage, and ramifies in the skin of the concave surface 

 of the ear. 



8. The digastric branch (R. digastricus) (Fig. 646) arises from the facial below 

 the auricular nerves and descends under cover of the parotid gland. Its branches 

 innervate the posterior belly of the digastricus, the stylo-hyoideus, and the occipito- 

 hyoideus. At its origin it gives off a small branch which forms a loop around the 

 great auricular artery or its posterior branch and rejoins the trunk. 



9. The auriculo-palpebral nerve (N. auriculopalpebralis) (Fig. 646) arises 

 from the upper edge of the facial near the posterior border of the ramus. It ascends 



^ Although this nerve springs directly from the gangUon, it contains motor as well as sensory 

 fibers. 



