THE CRANIAL NERVES 2/9 



perior rectus and levator palpebrae superioris; the inferior 

 separates into three branches, one of which is distributed to 

 the inferior rectus, another to the internal rectus, and a 

 third to the inferior oblique. From this last a branch is given 

 off to the lenticular ganglion to form its inferior root. 



Functions. This nerve has no function other than to 

 supply motion to the parts to which it is distributed. It is 

 insensible at its root, but receives filaments from the fifth 

 in the cavernous sinus, beyond which point stimulation pro- 

 duces pain as well as muscular contractions. The phenomena 

 sequent upon section of the nerve are suggested in its distri- 

 bution. ( i ) There is ptosis, or dropping of the upper lid ; 

 for the lid is kept open by the levator palpebrae superioris. 

 (2) There is external strabismus, because the external 

 rectus is not supplied by this nerve and is unopposed by the 

 internal rectus, the action of which is paralyzed. Diplopia 

 is the consequence. (3) There is inability to turn the ball 

 except in an outward direction because the muscles produc- 

 ing movements on the vertical and horizontal axes are de- 

 prived of innervation. (4) There is inability to rotate the 

 eye in certain directions on the antero-posterior axis. The 

 antagonist of the inferior oblique is the superior oblique, 

 the tendency of which latter is to rotate the globe so as to 

 make the pupil look downward and outward. When the 

 inferior oblique is paralyzed the superior oblique is unop- 

 posed, it is impossible to rotate the ball as is usual in side- 

 wise movements of the head, and double vision is the result. 

 (5) There is slight protrusion of the whole ball from relax- 

 ation of the muscles. (6) The pupil is dilated and move- 

 ments of the iris are interfered with. Stimulation of the 

 third nerve contracts the pupil, but when it is cut the pupil 

 does not respond to light. The ciliary nerves controlling 

 the movements of the iris come from the ophthalmic gang- 

 lion of the sympathetic ; to this ganglion goes a branch from 

 the third nerve. It is known that the action of the sympa- 

 thetic cannot be divorced from that of the cerebro-spinal 



