1484 ^ MANUAL OF ANATOMY 



of the eyeball, and terminates in an expansion which forms the 

 most internal layer of the retina, called the nerve-fibre or optic 

 layer. 



The optic nerve is the nerve of sight. 



Third or Oculo-motor Nerve.— The fibres of this nerve arise from 

 the oculo-motor nucleus, which is situated in the grey matter of the 

 ventral aspect (floor) of the aqueduct of Sylvius, on a level with 



M 



\ ; 



).i' 



■% 



\ 



Fig 619. — Scheme showing the Different Cell-groups which consti- 

 tute, ACCORDING TO PeRLIA, THE NUCLEUS OF OrIGIN OF THE ThIRD 



Cranial or Oculo-motor Nerve (L. Testut's ' Anatomie Humaine'). 



1. Posterfor Dorsal Nucleus 6. Antero-external Nucleus 



i'. Posterior Ventral Nucleus 7. Trunk of Oculo-Motor Nerve 



2. Anterior Dorsal Nucleus 8. Crossed Fibres 



2'. Anterior Ventral Nucleus 9. Fourth Cranial Nerve 



3. Central Nucleus 9'. Nucleus of Origin of Fourth Nerve 



4. Nucleus of Edinger and Westphal 9". Intercrossingof Fourth Cranial Nerves 



5. Antero-internal Nucleus 10. Third Ventricle 



M. Middle Line 



the upper quadrigeminal body, and extends superiorly, for a short 

 distance, on to the lateral wall of the third ventricle. The nucleus 

 is intimately related to the posterior longitudinal bundle, through 

 means of which it is connected with the trochlear and abducent 

 nuclei. All three nuclei receive collaterals from the posterior 

 longitudinal bundle ; and in this manner a functional association 

 between these nuclei is maintained, and harmonious action is 

 insured on the part of the muscles which are supplied by the nerves 



