1226 



HUMAN ANATOMY. 



exact relations of the Edinger-Westphal nucleus to the fibres of the third nerve are still unde- 

 termined, and, indeed, even its close association with these has been questioned. The assumed 

 importance of the nucleus as a centre for pupillary reflexes (Bernheimer) has been seriously 

 shaken by the recent observations of Tsuchida. ' This investigator also denies the existence 

 of a well marked and constant unpaired median nucleus as described by Perlia. but admits the 

 presence of broken groups of medially placed cells, especially in the upper and lower thirds o* 

 the nucleus. The lateral group of cells, beginning in the floor of the third ventricle and extend- 

 ing caudally as far as the upper third of the chief nucleus, constitutes the nucleus of Darksche- 

 witsch. Notwithstanding its proximity to the origin of the third nerve, this nucleus is now 

 regarded as having no direct relation with that of the oculomotor, but as standing in intimate asso- 

 ciation with the posterior longitudinal bundle, among whose fibres the cells to a large extent 

 lie ; it is, therefore, now often referred to as the nucleus fasciculi longitudinalis posterioris. 



Fig. 1051. 



<u 



•c 



V 



o 



R 

 u 



_ a 



dj o 



<u s 



o a 



'a o 



M 



u 

 u 



a 



■J) 



s 



u 



"- V. —•a U Da I, > Q, o. 

 \ \ \ \ *<3 .5 



ii 



t 



a 

 (J 



O. CD 



O tiS 



V 



s 

 .2* 



::: o 

 CO p 

 be o 



V 



£■3 

 U <?3 



^ 



Lachrymal 

 gland 



Levator palpe- 

 brae superioris 

 Superior 

 rectus muscle 



External rectus, 

 insertion 



Inferior oblique 

 muscle 



Cut surface of malar 

 bone 



Dissection of right orbit, showing oculomotor and abducent nerves. 



Although it may be assumed with much probability that the fibres destined for the different 

 eye-muscles originate from definite groups of nerve-cells, all attempts to locate with accuracy 

 the position of such centres within the oculomotor nucleus have met with only partial success. 

 Tsuchida's conclusions, based upon histological, embryological, comparative and clinical data, 

 point to an unexpected dif?useness in the origin of the oculomotor fibres with only a limited 

 relation to distinct groups. 



Concerning the mooted question as to the extent of decussation of the oculomotor fibres 

 it seems probable that such crossing occurs principally within the caudal portion of the 

 chief nuclei, although, according to Tsuchida and others, some decussating fibres are found 

 throughout the greater part of the nuclei. 



The fibres of the third nerve originate principally as the axones of the cells on 

 the same side, although a small number are derived from the neurones lying on the 

 opposite side of the mid-line. Some of these decussating fibres supply the internal 

 rectus and are related with the nucleus of the sixth nerve, which sends filxes by way 

 of the posterior longitudinal bundle into the oculomotor nucleus. Whether these 



' Arbeiten a. d. Hirnanatom. Institut in Zurich, Heft ii., 1906. 



