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.