760 THE NERVOUS SYSTEM 



(submaxillary) gland, and gives minute twigs to Wharton's duct, which accompany 

 the duct to its termination. From the fore part of the ganglion a branch passes to 

 the lingual nerve, and through this branch fibres from the chorda tympani are 

 conveyed to the sublingual gland and to the tongue. 



Sublingual ganglion. — A small ganglion has been described l)y Blandin an«l 

 others on the twig to the sublingual gland. According to Bose, it is not constant. 



Otic Gaxgliox 



The otic ganglion, or ganglion of Arnold, is a small reddish-grey body which 

 is placed innnediately l)elow the foramen ovale, internal to the mandibular division 

 of the trigeminal nerve. The cartilage of the Eustachian tube and the tensor 

 tympani muscle are placed close to its inner side, and the middle meningeal artery 

 is behind it. The ganglion is oval in form, and compressed in its coronal diameter. 

 It is greatest in its sagittal diameter, Avhicli is aljout four millimetres. 



Roots. — The mandibular division of the trigeminal nerve supplies one or mor(^ 

 roots to the otic ganglion; these roots probably contain both sensory and motor 

 fibres, and are associated with the nerve to the internal pterygoid. The lesser 

 superficial petrosal nerve enters the ganglion, being a motor root. The ganglion 

 receives a sympathetic root from the plexus which surrounds the middle 

 meningeal artery. 



Branches. — The otic ganglion furnishes muscular twigs to the tensor palatiand 

 tensor tympani; these twigs, especially the former, pass for the most part from the 

 mandibular division of the fifth nerve to the nuiscles without interrujition in the 

 nerve-cells of the ganglion. It also gives communicating branches to the auriculo- 

 temporal, the chorda tympani, and to the Vidian nerves. 



SIXTH OR ABDUCENT NERVE 



The sixth or abducent nerve arises from an ai)i)roximately spherical cluster of 

 nerve-cells which is i^Iaced l)etween the grey matter of the floor of the fourth 

 ventricle and the formatio reticularis. This nucleus is situated near the middle 

 line, a little in front of the striae acusticse, and corresponds to the eminentia teres. 

 It is on a line with the nuclei of the third and fourth nerves. The fibres which 

 arise from it plunge forwards and downwards through the substance of the pons, 

 and emerge at the lower border of the latter structvu-e (superficial origin). Some 

 of the fibres pass througli the pyramidal body; others pass out in the interval 

 between the latter and the olivary body. 



The stKth nerve was formerly described as giving fibres of origin to tLe facial, but Gudden 

 and (jrowers have shown that this is not the case. A remarkable strand of fibres passes from the 

 abdueens nucleus to the posterior longitudinal bundle. It runs brainwards, forming tlie inner 

 border of the bundle, and decussates below the corpora quadrigemina with its fellow of the 

 opposite side ; it then joins the third nerve, and passes eventually into the internal rectus muscle. 

 Thus the eyes can be directed to the right or left, as the case maj' be, by the action of a single 

 nucleus, e. g. in turning the eyes to the right, the right external rectus and the left internal 

 rectus are used, and these are both supplied by the right abducens nucleus. 



The sixth nerve pierces the dura mater at a point a little above the junction of 

 the basilar process of the occipital bone with the sjihenoid. It runs u})wards 

 between the pons and the V)ody of the sphenoid and at the side of the basilar artery, 

 and turns forwards in the interval between the apex of tlie petrous portion of the 

 temporal bone and the posterior clinoid process of the sphenoid, passing in this 

 situation under cover of a ligament which connects the osseous jirominences above 

 mentioned. It enters the flocH- of the cavernous sinus, and passes on to the outer 

 .side of the internal carotid artery. In this situation it receives several communi- 

 cations from the carotid plexus of the sympathetic. It enters the orbit through 

 the sphenoidal fissure, ])assing between the inferior division of the third nerve and 

 the ophthalmic vein, in the interval between the two heads of the external rectus 

 muscle, and ends by piercing the ocular surface of that muscle. 



