964 THE NERVOUS SYSTEM 



surface is separated by the dura mater from the temporal lobe of the brain, and the 

 lower rests upon the motor root of the fifth nerve and the outer layer of dura mater 

 upon the petrous portion of the temporal bone. 



The sensory root (portio major). The fibres of the sensory root, as they leave 

 the semilunar (Gasserian) ganglion, form from thirty to forty fasciculi which are 

 bound together into a flat band, from six to seven millimetres broad, which passes 

 backwards 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 backwards, medianwards, and downwards, and passes into 

 the pons through its continuation into the middle of the cerebellum. In the teg- 

 mentum of the pons region, the fibres bifurcate into ascending and descending 

 branches which terminate about the cells of the (sensory) nucleus of termination of 

 the trigeminus. This nucleus, large at the level of the entrance of the root, has a 

 tapering inferior extremity which 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. 



The motor root (portio minor). The fibres of the motor root of the fifth nerve 

 spring from two nuclei, a slender upper or mesencephalic nucleus, and a clustered 

 lower or principal nucleus. The fibres arising in the mesencephalic nucleus descend 

 along the lateral aspect of the nucleus to the pons as the descending or mesencephalic 

 root; here they join the fibres from the principal motor nucleus and issue with them 

 from the side of the pons in from six to ten fasciculi. The fasciculi blend to form the 

 motor root, which is from one and a half to two millimetres broad. At the point 

 where it emerges from the pons the motor root is in front of and ventral to the sen- 

 sory root, and it is separated from the latter by a few of the transverse fibres of the 

 pons which constitute the lingula of Wrisberg. From its superficial attachment 

 the motor root passes upwards, laterahvards, and forwards in the posterior fossa of 

 the cranium, and along the inner and anterior aspect of the sensory root, to the 

 mouth of Meckel's cave. In this cavity it runs laterahvards below the semilunar 

 (Gasserian) ganglion to the foramen ovale, through which it passes to join the mandi- 

 imlar nerve immediately below the base of the skull. 



Central Connections. The motor nuclei of the fifth nerve are connected with the lower 

 part of the somsesthetic area of the cerebral cortex of the opposite side by the genicular bundle of 

 pyramidal fibres, and they are associated with the sensory nuclei of other cranial nerves by the 

 medial longitudinal fasciculus. The sensory nuclei are connected with the somsesthetic area of the 

 cortex by the fibres of the medial lemniscus (fillet) and with the motor nuclei of other cranial 

 nerves by the medial longitudinal fasciculus. (For detailed central connections see pages 808, 

 810.) 



THE BRANCHES OF THE TRIGEMINUS 

 (1) THE OPHTHALMIC NERVE 



The ophthalmic nerve is exclusively sensory, and is the smallest of the three 

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

 inner part of the front of the ganglion and passes forwards, in the outer wall of the 

 cavernous sinus, where it lies below the fourth nerve and to the outer side of the 

 sixth nerve and the internal carotid artery (fig. 701). A short distance behind the 

 superior orbital (sphenoidal) fissure the nerve divides into three terminal branches 

 the frontal, lachrymal, and naso-ciliary (nasal) nerves. They pierce the dura mater, 

 which closes the fissure, and pass forwards into the orbit. Before its division the oph- 

 thalmic nerve receives communicating filaments from the cavernous plexus of the 

 sympathetic and it gives off, soon after its origin, a tentorial (recurrent meningeal) 

 branch which runs backwards, in close association with the fourth nerve, and ramifies 

 between the layers of the tentorium cerebelli. Further forwards three communica- 

 ting branches spring from the ophthalmic nerve and connect it with the third, fourth, 

 and sixth 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 outer side 

 of the fourth nerve. In the orbit it runs forwards, between the levator palpebrse supe- 

 rioris and the periosteum, and breaks up into three branches, the supra-orbital, 

 frontal proper, and supratrochlear. 



