BRANCHES OF THE TRIGEMINUS 935 



The semilunar (Gasserian) ganglion is a semilunar mass which lies in 

 ^vleckel's cave, a cleft in the dura mater above a depression in the medial part of 

 the upper surface of the petrous portion of the temporal bone. The convexity of 

 the ganglion is turned forward, and from it three large nerves, the ophthalmic, 

 the maxillary, and the mandibular, are given off. From the concavity, which is 

 directed backward, springs the root of the nerve. The medial end of the ganglion 

 is in close relation with the cavernous sinus and the internal carotid artery at the 

 foramen lacerum, and the lateral end lies to the medial side of the foramen ovale. 

 The surfaces of the ganglion are striated, due to bundles of fibres traversing them. 

 The upper surface is separated by the dura mater from the temporal lobe of the 

 brain, and the lower rests upon the masticator nerve and the outer layer of dura 

 mater upon the petrous portion of the temporal bone. 



The fibres of the trigeminus root as they leave the semilunar (Gasserian) ganghon, form from 

 thirty to forty fasciculi which are bound together into a flat band, from six to seven miUimetres 

 broad, which passes backward over the upper border of the petrous portion of the temporal 

 bone and below the superior petrosal sinus into the posterior fossa of the cranium. In the 

 posterior fossa it runs backward, medialward, and downward, and passes into the pons through 

 its continuation into the middle peduncle of the cerebellum. In the tegmentum of the pons 

 region, the fibres bifurcate into ascending and descending branches which terminate about 

 the cells of the nucleus of termination of the trigeminus. This nucleus, large at the level of 

 the entrance of the root, has tapering superior and inferior extremities. The inferior ex- 

 tremity of the nucleus, which is much the longer, descends as low as the upper portion of the 

 spinal cord and the fibres of the root terminating about the cells of this extremity are known 

 as the spinal tract of the trigeminus. 



Central connections. — The nuclei of termination of the trigeminus send impulses to the 

 somaesthetic area of the cortex of the opposite side by the fibres of the medial lemniscus (fillet) 

 and, for reflex actions, to the motor nuclei of other cranial nerves by the medial longitudinal 

 fasciculus and by fasciculi propri in the reticular formation of the same, and opposite sides. 



THE BRANCHES OF THE TRIGEMINUS 



The main branches of the trigeminus, given off by the front side of the semi- 

 lunar ganghon, are three in number (ophthalmic, maxillary, and mandibular), 

 each of which is referred to as a nerve and each of which is purely sensory, though 

 the third branch, or mandibular nerve, is joined by the fibres of the masticator 

 nerve which is motor. 



(1) The Ophthalmic Nerve or First Division 



The ophthalmic nerve, the first division of the trigeminus, is the smallest of the 

 three branches which arise from the semilunar (Gasserian) ganglion. It springs 

 from the medial part of the front of the ganglion and passes forward, in the lateral 

 wall of the cavernous sinus, where it lies below the trochlear nerve and lateral to 

 the abducens nerve and the internal carotid artery (fig. 734). A short distance 

 behind the superior orbital (sphenoidal) fissure the nerve divides into three ter- 

 minal branches — the frontal, lacrimal, and naso-ciliary (nasal) nerves. They 

 pierce the dura mater, which closes the fissure, and pass forward into the orbit. 

 Before its division the ophthalmic nerve receives filaments from the cavernous 

 plexus of the sympathetic and it gives off, soon after its origin, a tentorial (recur- 

 rent meningeal) branch which runs backward, in close association with the troch- 

 lear nerve, and ramifies between the layers of the tentorium cerebelli. Further 

 forward three branches spring from the ophthalmic nerve which contribute sen- 

 sory fibres to the oculo-motor, trochlear, and abducens nerves. 



The terminal branches. — (a) The frontal nerve is the largest terminal 

 branch. It pierces the dura mater and passes into the orbit through the superior 

 orbital (sphenoidal) fissure, above the rectus lateralis and a little below and to 

 the lateral side of the trochlear nerve. In the orbit it runs forward, between the 

 levator palpebrae superioris and the periosteum, and breaks up into three branches, 

 the supra-orbital, frontal proper, and supratrochlear. 



The supra-orbital nerve, the largest of the three branches, leaves the orbit at the supra- 

 orbital notch (fig. 734). As it passes through the notch it gives off a small branch which enters 

 the bone and supplies the diploe and the mucous membrane of the frontal sinus. Its terminal 

 branches give twigs to the pericranium and to the skin of the scalp, the upper eyehd, the frontal 



