THE CRANIAL NERVES 28l 



the pupil will look downward and outward. This move- 

 ment cannot be accomplished when the nerve is cut, and the 

 inferior oblique asserts itself unduly to bring about an op- 

 posite effect. The ball cannot accommodate itself to move- 

 ments of the head toward the shoulder, and double vision 

 supervenes -unless the object be brought in the involuntary 

 line of vision of the affected eye. 



Fifth Nerve (Trifacial, Trigeminus). 



The fifth is analogous to the spinal nerves (i) in rising 

 by two roots, (2) in having a ganglion on its posterior root, 

 and (3) in having a mixed function. The anterior root is 

 small and motor; the posterior large and sensory. 



Origin. Its apparent origin is from the side of the pons 

 above the median line. The deep origin of the large, sen- 

 sory root is in the pons immediately below the floor of the 

 fourth ventricle and just internal to its marginal boundary. 

 The small, motor root rises from a point just internal to the 

 large root. 



Course and Distribution. The two roots, taking their 

 origin as above described, pass through the dura above the 

 internal auditory meatus and run along the superior border 

 of the petrous portion of the temporal bone to a point near 

 its apex, where a large ganglion, the semilunar or Gasserian, 

 is developed on the posterior root and occupies a depression 

 on the bone for its reception. The motor root passes be- 

 neath the ganglion without being connected with it. 



The posterior root will be first followed to its distribu- 

 tion. 



From the anterior surface of the Gasserian ganglion are 

 given off three branches (i) ophthalmic, (2) superior 

 maxillary, (3) inferior maxillary. After the inferior max- 

 illary has left the cranial cavity it receives fibers from the 

 small or motor root, but the other branches are composed 

 entirely of fibers from the. sensory root. 



