516 ELEMENTARY PHYSIOLOGY less. 



of the brain and contains nerve cells. The proper olfac- 

 tory nerves are bundles of fibres which proceed from the 

 under surface of the above and traverse the cribriform 

 plate to be distributed to the olfactory mucous membrane. 

 And it is an extremely remarkable fact that these fibres 

 closely resemble the non-medulla,ted fibres of the sympa- 

 thetic nerves, in being hardly anything more than 

 neuraxes, bearing nuclei at intervals. A sheath, appar- 

 ently representing the neurilemma, is however present in 

 each fibre. 



The optic "nerve " is also properly speaking a lobe of 

 the brain, and it retains its chai-acter as a part of the 

 centi'al nervous system in so far as its fibres have no 

 neurilemma and are nodeless, but it contains no nerve cells 

 along its course. 



The third pair is called motor OCUli (mover of the 

 eye), because they are distributed to all the nmscles of the 

 eye except two. 



The nerves of the fourth pair, trochlear, and of the 

 sixth pair, abducens, supply, each, one of the muscles of 

 the eye, on each side ; the fourth going to the superior 

 oblique muscle, and the sixth to the external rectus. 

 Thus the muscles of the eye, small and close together as 

 they are, receive their nervous stimulus by three distinct 

 nerves. 



Each nerve of the fifth pair is very large. It has two 

 roots, a motor and a sensory, and further resembles a 

 spinal nerve in having a ganglion on its sensoiy root. It 

 is the nerve which supplies the skin of the face and the 

 muscles of the jaws, and, having three chief divisions, 

 is often called trigeminal. One branch containing 

 sensory fibres supplies the fore-part of the mucous 

 membrane of the tongue, and is often spoken of as the 

 gustatory. 



The seventh pair furnish with motor nerves the muscles 

 of the face, and some other muscles, and are called 

 facial. 



