THE FIFTH OR TRIFACIAL NERVE. 797 



third division is partly sensory and partly motor. It arises by two roots: of these 

 the anterior is the smaller, and is the motor root ; the posterior, the larger and 

 sensory. Its superficial origin is from the side of the pons Varolii, nearer to the 

 upper than the lower border. The smaller root consists of three or four bundles ; 

 the larger root consists of numerous bundles of fibres, varying in number from 

 seventy to a hundred. The two roots are separated from one another by a few of 

 the transverse fibres of the pons. The deep origin of the larger or sensory root 

 is from a nucleus in the pons, just below the floor and just internal to the mar- 

 gin of the upper half of the fourth ventricle. The deep origin of the smaller or 

 motor root is from a nucleus internal to the sensory root, and just external to the 

 fasciculus teres on the upper half of the floor of the fourth ventricle. The two 

 roots of the nerve pass forward through an oval opening (cavum Meckelit) in the 

 dura mater, on the superior border of the petrous portion of the temporal bone, 

 above the internal auditory meatus : they then run between the bone and the 

 dura mater to the apex of the petrous portion of the temporal bone, where the 

 fibres of the sensory root form a large, semilunar ganglion (G-asserian}, while the 

 motor root passes beneath the ganglion without having any connection with it, 

 and joins outside the cranium with one of the trunks derived from it. 



The Gasserian or semilunar ganglion * is lodged in a depression near the apex 

 of the petrous portion of the temporal bone. It is of somewhat crescentic form, 

 with its convexity turned forward. Its upper surface is intimately adherent to 

 the dura mater. Besides the small or motor root, the large superficial petrosal 

 nerve lies underneath the ganglion. 



Branches of Communication. This ganglion receives, on its inner side, fila- 

 ments from the carotid plexus of the sympathetic. Branches of Distribution. It 

 gives off minute branches to the tentorium cerebelli and the dura mater in the 

 middle fossa of me cranium. From its anterior border, which is directed forward 

 and outward, three large branches proceed the ophthalmic, superior maxillary, 

 and inferior maxillary. The ophthalmic and superior maxillary consist exclu- 

 sively of fibres derived from the larger root and ganglion, and are solely nerves 

 of common sensation. The third division, or inferior maxillary, is joined outside 

 the cranium by the motor root. This, therefore, strictly speaking, is the only 

 portion of the fifth nerve which can be said to resemble a spinal nerve. 



Ophthalmic Nerve (Figs. 384, 479, 481, 482, 486). 



The Ophthalmic, or first division of the fifth, is a sensory nerve. It supplies 

 the eyeball, the lachrymal gland, the mucous lining of the eye and nasal fossae, 

 and the integument of the eyebrow, forehead, and nose. It is the smallest of 

 the three divisions of the fifth, arising from the upper part of the Gasserian 

 ganglion. It is a short, flattened band, about an -inch in length, which passes 

 forward along the outer wall of the cavernous sinus, below the other nerves, and 

 just before entering the orbit, through the sphenoidal fissure, divides into three 

 branches lachrymal, frontal, and nasal. 



Branches of Communication. The ophthalmic nerve is joined by filaments 

 from the cavernous plexus of the sympathetic, communicates with the third and 

 sixth nerves, and is not unfrequently joined with the fourth. 



Branches of Distribution. It gives off recurrent filaments (nervi tentorii) 

 which pass between the layers of the tentorium along with a branch from the 

 fourth nerve, and then divides into 



Lachrymal. Frontal. Nasal. 



1 A Viennese anatomist, Raimund Balthasar Hirsch (1765), was the first who recognized the 

 ganglionic nature of the swelling on the sensory root of the fifth nerve, and called it, in honor of his 

 otherwise unknown teacher, Jon. Laur. Gasser, the " Ganglion Gasseri." Julius Casserius, whose 

 name is given to the musculo-cutaneous nerve of the arm, was professor at Padua, 1545-1605. (See 

 Hyrtl, Lehrbuch der Anatomie, p. 895 and p. 55.) 



