

THE ABDUCENT NERVE 



899 





Trigeminal Nerve Reflexes. Pains referred to various branches of the trigeminal nerve are of 

 very frequent occurrence, and should always lead to a careful examination in order to discover 

 a local cause. As a general rule the diffusion of pain over the various branches of the nerve is 

 at first confined to one only of the main divisions, and the search for the causative lesion should 

 always commence with a thorough examination of all those parts which are supplied by that 

 division; although in severe cases pain may radiate over the branches of the other main divisions. 

 The commonest example of this condition is the neuralgia which is so often associated with 

 dental caries here, although the tooth itself may not appear to be painful, the most distressing 

 referred pains may be experienced, and these are at once relieved by treatment directed to the 

 affected tooth. 



Many other examples of trigeminal reflexes could be quoted, but it will be sufficient to mention 

 the more common ones. Dealing with the ophthalmic nerve, severe supraorbital pain is com- 

 monly associated with acute glaucoma or with disease of the frontal or ethmoidal air cells. Malig- 

 nant growths or empyema of the maxillary antrum, or unhealthy conditions about the inferior 

 conchse or the septum of the nose, are often found giving rise to "second division" neuralgia, 

 and should be always looked for in the absence of dental disease in the maxilla. 



It is on the mandibular nerve, however, that some of the most striking reflexes are seen It 

 is quite common to meet with patients who complain of pain in the ear, in whom there is no sign 

 of aural disease, and the cause is usually to be found in a carious tooth in the mandible. More- 

 over, with an ulcer or cancer of the tongue, often the first pain to be experienced is one which 

 radiates to the ear and temporal fossa, over the distribution of the auriculotemporal nerve. 



THE ABDUCENT NERVE (N. ABDUCENS; SIXTH NERVE) (Fig. 777). 





The abducent nerve supplies the Rectus lateralis oculi. 



Its fibers arise from a small nucleus situated in the upper part of the rhomboid 

 fossa, close to the middle line and beneath the colliculus facialis. They pass down- 

 ward and forward through the pons, 

 and emerge in the furrow between the 

 lower border of the pons and the upper 

 end of the pyramid of the medulla ob- 

 longata. 



From the nucleus of the sixth nerve, 

 fibers are said to pass through the medial 

 longitudinal fasciculus to the oculomotor 

 nerve of the opposite side, along which 

 they are carried to the Rectus medialis. 

 The Rectus lateralis of one eye and the 

 Rectus medialis of the other may there- 

 fore be said to receive their nerves from 

 the same nucleus (Fig. 785). 



The nerve pierces the dura mater on 

 the dorsum sellse of the sphenoid, runs 

 through a notch in the bone below the 

 posterior clinoid process, and passes for- 

 ward through the cavernous sinus, on 

 the lateral side of the internal carotid 

 artery. It enters the orbit through the 

 superior orbital fissure, above the oph- 

 thalmic vein, from \vhich it is separated 

 by a lamina of dura mater. It then 

 passes between the two heads of the 

 Rectus lateralis, and enters the ocular 

 surface of that muscle. The abducent 

 nerve is joined by several filaments from 



the carotid and cavernous plexuses, and by one from the ophthalmic nerve. The 

 oculomotor, trochlear, ophthalmic, and abducent nerves bear certain relations to each 



Rectus lateralis- 



III. nerve-- 



VI. nerve- - 

 Nucleus III 



Nucleus VI. 



Rhomboid fossa 



FIG. 785. Figure showing the mode of innervation 

 of the Recti medialis and lateralis of the eye (after Duval 

 and Laborde). 



