THE HEAD AND NECK 



"53 



Third, or Oculo-motor, Nerve. — ^This nerve, having left the outer 

 wall of the cavernous sinus, breaks up at the sphenoidal fissure into 

 two divisions, upper and lower. These enter the orbit between 

 the t^vo heads of the external rectus muscle, the nasal nerve being 

 situated between the two. 



The tipper division furnishes two branches, which supply the 

 levator palpebral siiperioris and the superior rectus, the twigs 

 entering the muscles on their deep or ocular surfaces. 



The lower division, larger than the upper, furnishes three branches, 

 which supply the internal rectus, the inferior rectus, and the in- 

 ferior oblique. The twigs to the internal and inferior recti enter 

 these muscles on their deep or ocular surfaces. The branch to the 

 inferior oblique is a long nerve which passes forwards between the 

 inferior and external recti, and its twigs enter the inferior oblique 



Internal Rectus — 



Superior Oblique 

 Superior Rectus 



Levator Palpebrs 

 Superioris 



Sixth Nerve 



..Ciliary Nerves 



L.Optic Nerve (cut) 



External Rectus 



Branch of Third Nerve to 

 Inferior Oblique 

 Inferior Rectus 



Lower Division of Third Nerve 

 Upper Division of Third Nerve 

 Third Nerve 

 _. Internal Carotid Artery 



Fig. 



468. — The Third and Sixth Cranial Nerves in the Orbit 



(HiRSCHFELD AND LEVEILLfi). 



muscle at its posterior border. Posteriorly it furnishes the gang- 

 lionic branch, which forms the short or motor root of the lenticular 

 or ciliary ganglion. 



The fourth, trochlear, or pathetic nerve, of small size, having 

 left the wall of the cavernous sinus, enters the orbit through the 

 sphenoidal fissure above the muscles, and internal to, but on a 

 slightly higher plane than, the frontal nerve. Having passed 

 inwards over the levator palpebrae superioris, it enters the posterior 

 part of the superior oblique muscle on its superficial or orbital 

 surface, this being the only muscle which it supplies. 



The sixth or abducent nerve, having left the cavernous sinus, 

 enters the orbit through the sphenoidal fissure, and passes between 

 the tsvo heads of the external rectus muscle. In this situation it 

 has the lower division of the third ner\'e above it, and the ophthalmic 

 veins below it. It supplies the external rectus, its t\vigs entering 

 the muscle on its deep or ocular surface. 



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