886 NEUROLOGY 





of the sympathetic. In the superior orbital fissure it occasionally gives off a 

 branch to the lacrimal nerve. It gives off a recurrent branch which passes back- 

 ward between the layers of the tentorium cerebelli and divides into two or three 

 filaments which may be traced as far as the wall of the transverse sinus. 



THE TRIGEMINAL NERVE (N. TRIGEMINUS ; FIFTH OR TRIFACIAL 



NERVE). 



The trigeminal nerve is the largest cranial nerve and is the great sensory nerve 

 of the head and face, and the motor nerve of the muscles of mastication. 



It emerges from the side of the pons, near its upper border, by a small motor 

 and a large sensory root the former being situated in front of and medial to the 

 latter. 



Motor Root. The fibers of the motor root arise from two nuclei, a superior and 

 an inferior. The superior nucleus consists of a strand of cells occupying the whole 

 length of the lateral portion of the gray substance of the cerebral aqueduct. The 

 inferior or chief nucleus is situated in the upper part of the pons, close to its dorsal 

 surface, and along the line of the lateral margin of the rhomboid fossa. The fibers 

 from the superior nucleus constitute the mesencephalic root : they descend through 

 the mid-brain, and, entering the pons, join with the fibers from the lower 

 nucleus, and the motor root, thus formed, passes forward through the pons to its 

 point of emergence. It is uncertain whether the mesencephalic root is motor or 

 sensory. 



Sensory Root. The fibers of the sensory root arise from the cells of the semilunar 

 ganglion which lies in a cavity of the dura mater near the apex of the petrous part 

 of the temporal bone. They pass backward below the superior petrosal sinus 

 and tentorium cerebelli, and, entering the pons, divide into upper and lower roots. 

 The upper root ends partly in a nucleus which is situated in the pons lateral to the 

 lower motor nucleus, and partly in the locus cseruleus; the lower root descends 

 through the pons and medulla oblongata, and ends in the upper part of the sub- 

 stantia gelatinosa of Rolando. This lower root is sometimes named the spinal 

 root of the nerve. Medullation of the fibers of the sensory root begins about the 

 fifth month of fetal life, but the whole of its fibers are not medullated until the 

 third month after birth. 



The Semilunar Ganglion (ganglion semilunare [Gasseri] ; Gasserian ganglion) occu- 

 pies a cavity (cavum Meckelii) in the dura mater covering the trigeminal impression 

 near the apex of the petrous part of the temporal bone. It is somewhat crescentic in 

 shape, with its convexity directed forward : medially, it is in relation with the inter- 

 nal carotid artery and the posterior part of the cavernous sinus. The motor root 

 runs in front of and medial to the sensory root, and passes beneath the ganglion; 

 it leaves the skull through the foramen ovale, and, immediately below this 

 foramen, joins the mandibular nerve. The greater superficial petrosal nerve lies 

 also underneath the ganglion. 



The ganglion receives, on its medial side, filaments from the carotid plexus 

 of the sympathetic. It give off minute branches to the tentorium cerebelli, and to 

 the dura mater in the middle fossa of the cranium. From its convex border, which 

 is directed forward and lateral ward, three large nerves proceed, viz., the ophthalmic, 

 maxillary, and mandibular. The ophthalmic and maxillary consist exclusively 

 of sensory fibers ; the mandibular is joined outside the cranium by the motor root. 



Associated with the three divisions of the trigeminal nerve are four small ganglia. 

 The ciliary ganglion is connected with the ophthalmic nerve; the sphenopalatine 

 ganglion with the maxillary nerve; and the otic and submaxillary ganglia with the 

 mandibular nerve. All four receive sensory filaments from the trigeminal, and 



