748 



THE NERVOUS SYSTEM 



the posterior border of the inferior oblique. Near its commencement it gives off 

 the short or motor root to the lenticular ganglion. 



The third nerve supplies all the orbital muscles, with the exception of the 



Fig. 443.— Deep Origin of the Third Nerve. (After Krause. 



AQUEDUCT OF SYLVIUS 



DEHCEXDIXG 

 ROOT OF 

 TRIGEMINA L 

 NER VE 



NUCLEUS OF 

 THIRD NER VE 



POSTERIOR 

 LONGI- 

 TUDINAL 

 BUNDLE 



SUBSTANTIA 

 NIGRA 



i 



THIRD NERVE 



CRl STA 



external rectus and the superior oblique. It also supplies (through the lenticular 

 ganglion) the ciliary muscle and the circular fibres of the iris (sphincter iridis). 



In the wall of the cavernous sinus it is connected with the cavernous plexus of 

 the sympathetic and with the ophthalmic division of the fifth. 



FOURTH OR TROCHLEAR NERVE 



The fourth or trochlear nerve arises from a column of nerve-cells which is 

 continuous Avitli the nucleus of the third nerve. This column of cells is embedded 

 in the central grey matter below the aqueduct, and extends from the level of the 

 interval between the nates and testes to the lower margin of the latter bodies. 

 The nerve-fibres issuing from this elongated nucleus form two or three rounded 

 bundles, which run downwards, backwards, and slightly outwards along the outer 

 side of the nucleus, and then incline inwards to reach the valve of Vieussens, in 



