THE FIFTH, TRIGEMINAL, OR TRIFACIAL NERVE ('>79 



clalis) is the continuation of the parent trunk. It accompanies the ethmoidal 

 artery through the foramen of hke 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 in- 

 fratrochlear nerve (X. infratrochlearis) runs forward to th(^ inner canthus and rami- 

 fies 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; (6) 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 fil:)crs of the iris and the ciliary muscle are innervated by fibers derived from the 

 oculomotor nerve, the radial fil:)ers 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 oi)hthalmic nerve, with wdiich it is blended for some distance. 

 It emerges through the foramen rotundum, passes forward in the pterj^go-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 malae), 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 inter- 

 posed. It divides into posterior nasal, and greater and lesser i)alatine nerves. 



(1) The posterior nasal nerve (N. nasalis aboralis) passes through the sphenopala- 

 tine 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 sul)mucous 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 (X. palatinus major s. anterior) (Figs. 



