996 



THE NERVE SYSTEM 



is flushed into the opening at the external angle at frequent intervals. The stitches are removed 

 from the lid in from eight to ten days. 



The lingual nerve is occasionally divided with the view of relieving the pain in cancerous 

 disease of the tongue. This may be done in that part of its course where it lies below and behind 

 the last molar tooth. If a line is drawn from the middle of the crown of the last molar tooth to 

 the angle of the mandible, it will cross the nerve, which lies about half an inch behind the tooth, 

 parallel to the bulging alveolar ridge on the inner side of the body of the bone. If the knife is 

 entered three-quarters of an inch behind and below the last molar tooth and carried down to the 

 bone, the nerve will be divided. Hilton divided it opposite the second molar tooth, where it 

 is covered only by the mucous membrane, and Lucas pulls the tongue forward and over to the 

 opposite side, when the nerve can be seen standing out as a firm cord under the mucous mem- 

 brane by the side of the tongue and can be easily seized with a sharp hook and divided or a 

 portion excised. This is a simple enough operation on the cadaver, but when the disease is 

 extensive and has extended to the floor of the mouth, as is generally the case when division of 

 the nerve is thought of, the operation is not practicable. 



Fi-ontal. 



Lacrimal 



THE SIXTH OR ABDUCENT NERVE (N. ABDUCENS) (Fig. 733). 



The sixth or abducent nerve supplies the External rectus muscle. Its super- 

 ficial origin is by several filaments from the postpontile groove, between pons and 

 pyramid. Its deep origin is from the upper part of the floor of the fourth ventricle, 

 close to the median line, beneath the eminentia abducentis (Fig. 648). From the 

 nucleus of the abducent nerve some fibres are supposed to pass through the 

 medial longitudinal bundle to the oculomotor nucleus of the opposite side and 

 into the oculomotor nerve, along which they are carried to the Internal rectus 

 muscle. See, however, the description already given on page 903. 



The nerve pierces the dura on the basilar surface of the sphenoid bone, runs 

 through a notch immediately below the posterior clinoid process, and enters the 

 cavernous sinus. It passes forward through the sinus, lying on the outer side 

 of the internal carotid artery (Fig. 505). It enters the orbit through the sphenoidal 



fissure, and lies above the oph- 

 thalmic vein, from which it is 

 separated by a lamina of dura 

 (Fig. 738). It then passes be- 

 tween the two heads of the 

 External rectus muscle, and is 

 distributed to that muscle on 

 its ocular surface. 



Branches of Communication. 

 It is joined by several fila- 

 ments from the carotid and 

 cavernous plexuses, and by 

 one from the ophthalmic nerve. 

 Relations to One Another of 

 the Oculomotor, Trochlear, Oph- 

 thalmic Division of the Trigeminal, and Abducent Nerves as they Pass to the Orbit. 

 -The oculomotor, trochlear, the ophthalmic division of the trigeminal, and the 

 abducent nerves, as they pass to the orbit, bear a certain relation to one another 

 in the cavernous sinus, at the sphenoidal fissure, and in the cavity of the orbit, 

 which will now be described. 



In the cavernous sinus (Figs. 505 and 506) the oculomotor, trochlear, and 

 ophthalmic division of the trigeminal are placed on the outer wall of the sinus, 

 in their numerical order, both from above downward and from within outward. 

 The abducent nerve lies at the outer side of the internal carotid artery. As these 

 nerves pass forward to the sphenoidal fissure, the oculomotor and trigeminal 

 nerves become divided into branches, and the abducent nerve approaches the rest 

 so that their relative position becomes considerably changed. 



Superior division of oculo-motor. 

 '/Nasal. 



'Inferior division of oculo-molor- 

 "Abducent. 

 'Ophthalmic vein. 



FIG. 738. Relations of structures passing through the 

 sphenoidal fissure. 



