Part 80

1. =N. ophthalmicus.=--The ophthalmic or first division of the fifth nerve arises from the semilunar (or Gasserian) ganglion. It passes out of the cranial cavity and into the orbit by way of the orbital fissure, in company with the third, fourth, and sixth nerves and with the extension of the carotid (arterial) plexus.

It passes between the superior and medial recti along with the third nerve, crosses dorsad of the optic nerve, and divides into =infratrochlear= and =ethmoidal= branches. In the orbital fissure it gives off the =frontal= nerve, and while crossing the optic it gives off the =long ciliary= nerve.

a. =N. frontalis.=--The frontal nerve passes along the lateral border of the superior oblique muscle and then laterad of the pulley to near the middle of the supraorbital crest of the frontal bone. Here it passes out of the orbit and is distributed to the integument of the upper eyelid and the adjacent region at the side of the nose.

b. =N. infratrochlearis.=--The infratrochlear nerve passes between the superior rectus and the superior oblique in the first part of its course. It then passes ventrad of the superior oblique and ventrad of the pulley to be distributed to the integument of the upper eyelid near the inner angle.

c. =N. ethmoidalis.=--The ethmoidal nerve passes along with the ethmoidal artery through the ethmoidal foramen (or foramina) in the orbital plate of the frontal bone. It is finally distributed to the mucosa of the nose and to the cartilage and integument of the snout.

d. =N. ciliaris longus.=--The long ciliary nerve arises from the ophthalmic and passes along the optic nerve to be distributed to the eyeball. It divides into several branches before penetrating the sclerotic.

One or two small communicating branches to the =ciliary ganglion= are given off at about the same point as the long ciliary nerve. (For a description of this ganglion see the account of the oculomotor nerve, page 369.)

2. =N. maxillaris.=--The maxillary nerve, the second division of N. trigeminus, rises from the semilunar (Gasserian) ganglion and leaves the skull by the foramen rotundum. It is the sensory nerve of the palate, upper teeth and upper lip, and of part of the forehead and cheek.

On leaving the foramen the maxillary nerve divides into three branches, the two =infraorbital= nerves (Fig. 154, f) and the =sphenopalatine= (Fig. 154, g). Two smaller branches are likewise given off either within or just outside of the foramen, the =lachrymal= nerve (Fig. 154, j) and the =zygomatic= (subcutaneus malæ) (Fig. 154, i).

a. =N. lachrymalis= (Fig. 154, j; Fig. 155, m).--The lachrymal nerve passes along the periorbita to the lachrymal gland (Fig. 154, 11), to which it gives branches. It then continues caudad of the zygomatic process of the temporal to the integument; here it turns caudad and is distributed to the integument in the region between the eye and the external ear (Fig. 155, m). It anastomoses with the zygomatic branch of the seventh nerve (Fig. 155, h).

b. =N. zygomaticus= (subcutaneus malæ) (Fig. 154, i).--This arises with the preceding and follows it for some distance. It passes through a foramen in the frontal process of the malar bone and is distributed to the lower eyelid and adjacent integument.

c. =Nn. infraorbitales= (Fig. 154, f; Fig. 155, l).--The infraorbital nerves are two of nearly equal size. They pass through the orbit ventrad of the eyeball to the infraorbital canal. On their course each divides once or twice and each divides again in the infraorbital foramen, so that about eight branches emerge from the infraorbital foramen and diverge to the integument and whiskers of the upper lip and to the side and wing of the nose (Fig. 155, l). In the infraorbital canal, and before reaching it, branches are given to the molar teeth, and a branch continues in the bone to the canine, incisor, and premolar teeth.

d. =N. sphenopalatinus= (Fig. 154, g).--The sphenopalatine nerve turns mediad from the infraorbitals, directing its course toward the sphenopalatine foramen. Before reaching this it gives off the =greater palatine= nerve (=N. palatinus major=), which enters the posterior palatine canal and passes to the hard palate. The sphenopalatine then usually divides into two branches which pass along side by side to enter the =sphenopalatine ganglion=. This is a large elongated triangular ganglion lying on the dorsal surface of the external pterygoid muscle, just laterad of the sphenopalatine foramen.

The following nerves are connected with the sphenopalatine ganglion:

a. =N. palatinus minor.=--This leaves the craniolateral angle of the ganglion and passes to the soft palate.

b. =N. nasalis posterior.=--The posterior nasal nerve enters the nasal cavity by the sphenopalatine foramen and is distributed to the mucosa of the ventral and middle parts of the nasal cavity.

c. =N. canalis pterygoidii= (Vidian Nerve).--This is a large nerve which leaves the caudal angle of the sphenopalatine ganglion and passes caudad. It enters the orbital fissure, lying in a groove on its ventral wall (the cranial end of this groove is sometimes converted into a canal). The groove ends caudally in a foramen which pierces the sphenoid bone between the wing and the body and lies just mediad of the foramen rotundum. The groove and foramen constitute the pterygoid canal (from which the nerve is named). After emerging from the pterygoid canal onto the ventral surface of the basisphenoid the nerve enters the tympanic bulla along with the Eustachian tube, lying on the medial side of the latter. Just after entering, on reaching the internal carotid artery, it divides into two. One of these, =N. petrosus superficialis major= (p. 375), passes into the hiatus facialis of the petrous bone and joins the facial nerve. The other, =N. petrosus profundus=, accompanies the internal carotid artery caudad, turning therefore out of the bulla and passing caudad along its medial side; it finally joins the superior cervical ganglion of the sympathetic system.

3. =N. mandibularis.=--The third division of the fifth, the mandibular nerve, takes origin by a strong root from the semilunar (or Gasserian) ganglion, and receives also after separating from the ganglion the smaller ventral root (portio minor) of the fifth nerve. The root from the ganglion is sensory; the smaller root is motor, so that the mandibular nerve is both sensory and motor. The nerve passes through the foramen ovale, and sends off at once the following branches:

a. =N. auriculotemporalis= (Figs. 154 and 155, n).--This passes dorsad between the cartilaginous auditory meatus and the zygomatic process of the temporal bone (Fig. 154, n), emerges at the caudal border of the masseter muscle (Fig. 155, n), and divides into two chief branches. One, the =auricular= branch, passes along the cranial side of the external ear and is distributed to its integument. The other, the =temporal= branch, passes along the zygomatic arch, gives branches to the temporal muscle and to the skin, follows the zygomatic arch almost to the angle of the mouth, and anastomoses with the superior buccal branch of the facial (Fig. 155, k).

b. =N. temporalis profundus.=--One or more large branches passing mediad of the zygomatic arch to the temporal muscle.

c. =N. massetericus.=--The masseteric nerve passes dorsocraniad to the masseter muscle.

d. =N. pterygoideus.=--One or more pterygoid branches pass to the pterygoid muscles. A small twig from the nerve to the internal pterygoid passes into the tympanic cavity and supplies the tensor tympani muscle.

e. =N. buccinatorius= (Fig. 154, e).--This passes craniad along the dorsolateral surface of the pterygoid muscles (Fig. 154, 8) to the angle of the mouth. Here it divides into branches to the masseter muscle, the mucosa of the mouth, and to the lips.

The mandible and zygomatic arch have been cut and removed; the temporal and internal pterygoid muscles are also removed. a, N. hypoglossus; b, N. lingualis; c, N. chorda tympani; d, N. alveolaris inferior (cut); e, N. buccinatorius; f, Nn. infraorbitales; g, N. sphenopalatinus; h, branch of N. oculomotorius; i, N. zygomaticus; j, N. lachrymalis; k, N. abducens; l, N. trochlearis; m, N. frontalis; n, N. auriculotemporalis. 1, cut end of zygomatic process of temporal; 2, tympanic bulla; 3, M. digastricus; 4, M. constrictor pharyngis medius; 5, M. hyoglossus; 6, M. genioglossus; 7, M. geniohyoideus; 8, M. pterygoideus externus (cut); 9, cut cranial end of zygomatic arch; 10, mandible (cut); 11, lachrymal gland.]

After giving off the above branches the mandibular nerve passes three or four millimeters laterad along the root of the zygomatic process of the temporal bone, and divides into two large branches, the =inferior alveolar= (or dental) nerve (d) and the =lingual= nerve (b).

f. =N. alveolaris inferior= (Fig. 154, d).--This passes toward the mandibular foramen, but before reaching it gives off a branch to the mylohyoid and digastric muscles. It then enters the foramen, passes through the mandibular canal, and gives numerous =inferior dental= branches to the teeth. At the mental foramen (or foramina) it passes out of the canal and divides into several =mental= nerves, to the chin, lower lip, and mucosa of the lower jaw.

g. =N. lingualis= (Fig. 154, b).--The lingual nerve passes between the internal and external pterygoid muscles, and two or three millimeters from its origin it receives the =chorda tympani= nerve (c), a communicating branch from the facial (see page 376). It passes onto the ventral surface of the external pterygoid, thence onto the side of the tongue, beneath the mylohyoid. On the side of the tongue it divides into branches which enter the tongue and are distributed to its mucous membrane. One branch passes to the mucosa of the pharynx. Just before entering the tongue a branch is given off to the sublingual and submaxillary glands.

VI. N. ABDUCENS.--The sixth nerve, the abducens, arises from the medulla, as already described (Fig. 138, VI, and page 347). It passes into the orbit through the orbital fissure, then extends obliquely cranioventrad along the medial surface of the lateral rectus muscle (Fig. 154, k). At about the middle of the length of the muscle it divides into two or three branches which enter at once into the lateral rectus and supply it.