OCULOMOTOR NUCLEUS. 



NUCl. EDINSER- NUCL.MED. 



The nucleus from which the third nerve takes origin extends upwards underneath 

 the superior corpora quadrigemina, ventral to the Sylvian aqueduct, and even extends 

 into a corresponding situation in the posterior part of the third ventricle. The 

 anterior (superior) part is composed of smaller cells than the other portion : it 

 extends forwards into the wall of the third ventricle, and from the experiments of 

 Hensen and Voelckers and the observations of Starr, it appears to be subdivided 

 into two portions, of which that which is the more mesial, and lies just above the 

 corpora mamillaria, is connected Avith the fibres of the third nerve to the ciliary 

 muscle, whilst that which is the more lateral is connected with the fibres concerned 

 with the contraction of the sphincter pupillge. The main part of the oculomotor 

 nucleus is formed by large cells, which tend to be grouped (see diagram, fig. 74). 

 Thus, there are two distinct groups on each side which are dorso-lateral (dorsal 

 nuclei), and two which are ventro-mesial (ventral nuclei). These four nuclei are 

 grouped around a central nucleus which lies in the middle line. Besides these, 

 there is an elongated nucleus of small cells which inferiorly (caudalwards) 

 lies in close contact with the cen- 

 tral nucleus but superiorly curves 

 outwards. This is known as the 

 nucleus of Edinger and Westphal, 

 but it is uncertain whether it gives 

 origin to any fibres of the third 

 nerve. It has not been certainly 

 ascertained from which of the seve- 

 ral groups the fibres to particular 

 muscles moving the globe of the eye 

 proceed. From the several groups 

 of cells which constitute the oculo- 

 motor nucleus the fibres of the third 

 nerve pass with a curved course 

 through the tegmentum, to emerge 

 at the inner margin of the crusta of 

 the same side ; but the fibres from 

 the posterior of the dorsal groups 

 undergo decussation. These fibres 

 are believed to pass to the internal 

 rectus of the opposite side. 



NUCi. LAT. ANT 

 fOARKSCMEWITiCH) 



NUCL.OORS.I.(AM-~, 



nUCL.VENT.I. (NT.)-__ 



NUCL.OORS.II.C'OST) 

 (V.G-UDDEN) 



NUCL. CEMTRALIS-' 



NUCU.VENT.II.(POST.) 



Fig. 74. DIAGRAM OP THE GROUPS OF CELLS FORMING 



THE NUCLEI OF THE THIRD AND FOURTH NERVES. 



(Perlia.) 



In a case recorded by Kahler and 

 Pick, in which there was paralysis of 

 the levator palpebrae, the rectus superior 

 and the obliquus inferior, a lesion was 



found involving the postero-lateral bundle of the nerve-roots. The observations of Starr point 

 to these three muscles being innervated from the dorsal (dorso-lateral) groups, and the rectus 

 internus and rectus inferior from the ventral (ventro-mesial) groups, in the order here given 

 (from above down). 



It has been shown by Duval and Laborde that the third nerve receives fibres 

 from the mesial part of the posterior longitudinal bundle of the opposite side 

 (possibly some fibres also pass to it from the posterior longitudinal bundle of the same 

 side). These fibres are derived mainly from the nucleus of the sixth nerve, and pass 

 out along with the fibres of the third nerve to the internal rectus, so that the nucleus 

 of the sixth thus supplies both the external rectus of the same side entirely, and the 

 internal rectus of the opposite side partially (fibres derived from the nucleus of the 

 third also going to the internal rectus). These are, it may be noted, the muscles 

 which are brought together into action in con^ug-ate; dbyiatioii of' the cye&tq eidBe,r 



' ' 



