Part 205

I. The =ophthalmic nerve= (N. ophthalmicus) (Figs. 438, 439, 440) is purely sensory and is the smallest of the three branches of the trigeminus. It arises from the inner part of the front of the semilunar ganglion, passes forward along the outer side of the cavernous sinus, and is blended with the maxillary nerve for some distance. It enters the foramen lacerum orbitale with the third and sixth nerves and divides into three branches.

1. The =lacrimal nerve= (N. lacrimalis) runs forward on the rectus superior and the levator palpebræ superioris and ramifies chiefly in the lacrimal gland and the upper eyelid. A branch (Ramus zygomatico-temporalis) exchanges twigs with the zygomatic branch of the maxillary nerve, perforates the periorbita, and emerges from the orbital fossa behind the supraorbital process; it forms a plexus with branches of the auriculo-palpebral and frontal nerves, and ramifies in the skin of the temporal region.

2. The =frontal nerve= (N. frontalis), also termed the supraorbital, runs forward almost parallel with the superior oblique muscle, at first within, then outside of, the periorbita. It passes through the supraorbital foramen with the artery of like name and ramifies in the skin of the forehead and upper eyelid, forming a plexus with the lacrimal and auriculo-palpebral nerves. It divides into three branches.

3. The =naso-ciliary nerve= (N. naso-ciliaris), also termed the palpebro-nasal, runs forward along the inner side of the optic nerve between parts of the retractor muscle and divides into two branches. Of these the =ethmoidal nerve= (N. ethmoidalis) is the continuation of the parent trunk. It accompanies the ethmoidal artery through the foramen of like name into the cranial cavity and crosses the lower part of the ethmoidal fossa. Leaving the cranium through an opening in the cribriform plate close to the crista galli, it enters the nasal cavity and ramifies in the mucous membrane of the septum nasi and the superior turbinal. The =infratrochlear nerve= (N. infratrochlearis) runs forward to the inner canthus and ramifies in the skin in this region; it detaches twigs to the conjunctiva and caruncula lacrimalis, and a long branch which supplies the third eyelid and the lacrimal ducts and sac. The naso-ciliary nerve furnishes the =sensory= or =long root= (Radix longa) of the ciliary ganglion.

The =ciliary ganglion= is placed on the inferior branch of the oculomotor nerve. It is usually not larger than a millet-seed, and is best found by following the nerve to the inferior oblique muscle back to its origin. The ganglion receives (a) =sensory fibers= from the naso-ciliary nerve; (b) =motor fibers= from the oculomotor nerve; and (c) =sympathetic fibers= from the sphenopalatine plexus. It detaches filaments which unite with twigs from the ophthalmic and maxillary nerves and from the sphenopalatine ganglion to form the ciliary plexus. From the latter emanate five to eight delicate =short ciliary nerves= (Nn. ciliares breves), which pursue a somewhat flexuous course along the optic nerve, pierce the sclera near the entrance of that nerve, and run forward between the sclera and chorioidea to the circumference of the iris. Here the branches of adjacent nerves anastomose to form a circular plexus (Plexus gangliosus ciliaris), from which filaments go to the ciliary body, iris, and cornea.

The circular fibers of the iris and the ciliary muscle are innervated by fibers derived from the oculomotor nerve, the radial fibers of the iris by the sympathetic.

II. The =maxillary nerve= (N. maxillaris), also termed the superior maxillary, is purely sensory and is much larger than the ophthalmic. It extends forward from the semilunar ganglion in the middle cranial fossa in the large groove on the root of the temporal wing of the sphenoid. It is related internally to the cavernous sinus and superiorly to the ophthalmic nerve, with which it is blended for some distance. It emerges through the foramen rotundum, passes forward in the pterygo-palatine fossa above the internal maxillary artery and embedded in fat, and is continued in the infraorbital canal as the infraorbital nerve (Fig. 439). Its branches are as follows:

1. The =zygomatic nerve= (N. zygomaticus s. subcutaneus malæ), also termed the orbital branch, arises before the maxillary nerve reaches the pterygo-palatine fossa (Figs. 438, 439, 514). It pierces the periorbita and divides into two or three delicate branches which pass along the surface of the external straight muscle to the external canthus and ramify chiefly in the lower lid and the adjacent skin. Anastomoses are formed with branches of the lacrimal nerve.

2. The =sphenopalatine nerve= (N. sphenopalatinus) is given off in the pterygo-palatine fossa from the lower border of the maxillary nerve (Fig. 439). It is broad and flat and forms a plexus in which several small =sphenopalatine ganglia= are interposed. It divides into posterior nasal, and greater and lesser palatine nerves. (1) The =posterior nasal nerve= (N. nasalis aboralis) passes through the sphenopalatine foramen, in which it bears one or more minute ganglia, enters the nasal cavity, and divides into internal and external branches (Figs. 440, 464). The internal branch (N. septi narium) runs forward in the submucous tissue of the lower part of the septum nasi, gives twigs to the mucous membrane here and to the vomero-nasal organ (of Jacobson), passes through the palatine cleft and ramifies in the anterior part of the hard palate. The external branch (Ramus lateralis) ramifies in the mucous membrane of the inferior turbinal and the middle and inferior meatus nasi. (2) The =greater= or =anterior palatine nerve= (N. palatinus major s. anterior) (Figs. 438, 439) is the largest of the three branches. It runs forward in the palatine canal and groove and ramifies in the hard palate and gums. It also supplies twigs to the soft palate, and gives off branches which pass through the accessory palatine foramina to supply the mucous membrane of the inferior meatus.

The branches of the two nerves anastomose in the hard palate and form a plexus about the branches of the palatine arteries.

FIG. 514.—DISSECTION OF HEAD OF HORSE.

The masseter and superficial muscles and the parotid gland are in great part removed. a, a, Levator labii superioris proprius; b, b, levator nasolabialis; c, dilatator naris inferior; d, buccinator; e, common mass of buccinator and depressor labii inferioris; f, depressor labii inferioris; g, masseter; h, orbicularis oculi; i, temporalis; k, occipito-hyoideus; k′, stylo-maxillaris; l, sterno-cephalicus; l′, tendon of same; m, omo-hyoideus; n, crico-pharyngeus; o, mastoid tendon of mastoido-humeralis; p, splenius; q, inferior buccal and labial glands; r, superior buccal glands; s, remnant of parotid gland; t, submaxillary gland; u, anterior cervical (subparotid) lymph glands; v, probe passed into diverticulum nasi; w, cornu of alar cartilage; x, internal palpebral ligament; y, wing of atlas; z, scutiform cartilage of ear; 1, external nasal nerve; 2, anterior nasal nerve; 3, superior labial nerve; 4, anterior part of superior buccal nerve; 5, buccinator nerve; 6, 6′, inferior alveolar nerve; 6″, mental nerve-continuation of 6; 7, masseteric nerve; 8, facial nerve (cut); 9, superficial temporal nerve; 10, anastomosis between 9 and 8; 11, internal auricular nerve; 12, posterior auricular nerve; 13, digastric nerve; 14, cervical branch of facial nerve (cut); 15, auriculo-palpebral nerve; 16, lacrimal nerve; 17, frontal nerve; 18, infratrochlear nerve; 19, n. zygomaticus s. subcutaneus malæ; 20, spinal accessory nerve; 21, ventral branch of spinal accessory nerve (to sterno-cephalicus); 22, ventral end branch of first cervical nerve; 23, thyro-laryngeal artery; 24, internal maxillary artery; 25, masseteric artery; 26, great (posterior) auricular artery; 27, external branch of 26; 28, deep auricular artery; 29, superficial temporal artery; 30, transverse facial artery; 31, facial artery; 32, inferior labial artery; 33, superior labial artery; 34, lateral nasal artery; 35, dorsal nasal artery; 36, angular artery of eye; 37, labial twigs of palato-labial artery—left uncolored by oversight; 38, branch of buccinator artery; 39, buccinator vein; 40, vena reflexa; 41, 42, jugular vein; 43, external maxillary vein; 44, inferior cerebral vein; 45, stump of great auricular vein; 46, ramus of mandible; 47, facial crest; 48, zygomatic arch; 49, parotid duct. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) ]

(3) The =lesser= or =posterior palatine nerve= (N. palatinus minor s. posterior), also termed the staphyline, is much the smallest of the three branches (Figs. 438, 439). It passes downward and forward with the palatine vein in the groove at the inner side of the tuber maxillare and ramifies in the soft palate.

The sphenopalatine ganglia and plexus (Fig. 515) lie on the perpendicular part of the palate bone and the pterygoid process under cover of the maxillary nerve. The afferent fibers of the plexus and ganglia come chiefly from the branches of the sphenopalatine nerve and the nerve of the pterygoid canal. Interspersed in these are several minute ganglia and one or more larger ones. The =nerve of the pterygoid canal= or =Vidian nerve= (N. canalis pterygoidei) is formed by the union of sympathetic fibers with the superficial petrosal branch of the facial nerve. It passes forward at first between the Eustachian tube and the sphenoid bone, enters the canal between the pterygoid bone and process, and joins the posterior part of the plexus. It is probable that it furnishes the motor fibers to the levator palati and palatinus muscles. Efferent filaments go to the periorbita and the ophthalmic vessels, and others accompany the branches of the maxillary nerve, around which they have a plexiform arrangement.

3. The =infraorbital nerve= (N. infraorbitalis) is the continuation of the maxillary trunk. It traverses the infraorbital canal, emerges through the infraorbital foramen, and divides into nasal and superior labial branches. Along its course it gives off =superior alveolar= or =dental branches= (Rami alveolares maxillæ), which supply the teeth, alveolar periosteum, and gums.

The delicate posterior alveolar branches are given off in the pterygo-palatine fossa, pass through small foramina in the tuber maxillare, and supply the posterior molar teeth and the maxillary sinus. The middle alveolar branches are given off in the infraorbital canal, and constitute the chief nerve-supply to the cheek teeth and the maxillary sinus. The anterior or incisor branch runs forward in the anterior alveolar or incisor canal and supplies branches to the canine and incisor teeth. The foregoing unite with each other to form the superior dental plexus, from which the dental and gingival branches are given off.

The =external nasal branches= (Rami nasales externi), two or three in number, accompany the levator labii superioris proprius and ramify in the dorsum nasi and the nasal diverticulum.

The large =anterior nasal branch= (Ramus nasalis anterior) passes over the nasal process of the premaxilla under cover of the dilatator naris inferior, gives branches to the nasal mucous membrane, and terminates in the skin of the upper lip.

The =superior labial branch= (Ramus labialis dorsalis) is the largest of the terminals of the infraorbital nerve. It passes downward and forward under the levator nasolabialis and, after supplying the skin of the anterior part of the cheek, forms a rich terminal ramification in the skin and mucous membrane of the upper lip. It anastomoses with the superior buccal branch of the facial nerve.

III. The =mandibular nerve= (N. mandibularis), also termed the inferior maxillary branch, is formed by the union of two roots; of these the large sensory root comes from the semilunar ganglion, and the small motor root is the pars minor of the trigeminus. It emerges from the cranium through the oval notch of the foramen lacerum, between the temporal wing of the sphenoid bone and the muscular process of the petrous temporal, and gives off the following branches:

1. The =masseteric nerve= (N. massetericus) (Figs. 437, 515) passes outward through the sigmoid notch of the mandible and enters the deep face of the masseter muscle, in which it ramifies.

2. The =deep temporal nerves= (Nn. temporales profundi) (Fig. 437), two or three in number, arise by a common trunk with the masseteric. They supply the temporal muscle.

3. The =buccinator nerve= (N. buccinatorius) passes obliquely forward through the anterior part of the external pterygoid muscle, then between the internal pterygoid and the tuber maxillare (Fig. 514). It continues forward in the submucous tissue of the cheek along the lower border of the buccinator and divides into branches which ramify in the mucous membrane and glands of the lips in the vicinity of the commissure. It supplies small branches to the external pterygoid and temporal muscles and detaches numerous collateral twigs to the mucous membrane of the cheek and to the buccal glands. It also communicates with the inferior buccal branch of the facial nerve.

4. The =pterygoid nerve= (N. pterygoideus) arises in common with the preceding, passes forward on the guttural pouch, and divides into branches for the pterygoid muscles (Fig. 515).

The =otic ganglion= (G. oticum) is situated near the origin of the pterygoid and buccinator nerves, and is related internally to the tensor palati and the Eustachian tube. It receives motor fibers from the pterygoid nerve and sensory fibers by the small superficial petrosal nerve from the tympanic plexus, through which communications are made with the facial and glosso-pharyngeal nerves. Sympathetic fibers are derived from the plexus on the internal maxillary artery. Efferent filaments go to the tensor palati, tensor tympani, and pterygoid muscles, and to the Eustachian tube.

The ganglion is small and somewhat difficult to demonstrate. In many cases it is replaced by a number of minute ganglia interspersed in a fine plexus.

5. The =superficial temporal nerve= (N. temporalis superficialis) (Figs. 437, 514, 515) runs outward across the pterygoideus externus, passes between the parotid gland and the neck of the ramus of the mandible, turns around the latter, and divides into two branches. The upper branch (Ramus transversus faciei) accompanies the transverse facial vessels and ramifies in the skin of the cheek. The larger inferior branch unites with the inferior buccal division of the facial nerve.

FIG. 515.—DEEP DISSECTION OF BASE OF CRANIUM, VIEWED FROM THE RIGHT AND BELOW.