136 NEKVOTJS SYSTEM. 



ascertained by Longet 1 and by Chauveau. 3 The question 

 of the function of the nerve, therefore, resolves itself sim- 

 ply into the mode of action of the superior oblique muscle. 

 This muscle arises just above the inner margin of the optic 

 foramen, passes forward, along the upper wall of the orbit 

 at its inner angle, to a little cartilaginous ring which serves 

 as a pulley. From its origin to this point it is muscular. 

 Its tendon becomes rounded just before it passes through 

 the pulley, where it makes a sharp curve, passes outward 

 and slightly backward, and becomes spread out to be at- 

 tached to the globe at the superior and external part of its 

 posterior hemisphere. It acts upon the eyeball from the 

 pulley at the upper and inner portion of the orbit as the 

 fixed point, and rotates the eye upon an oblique, horizontal 

 axis, from below upward, from without inward, and from 

 behind forward. By its action, the pupil is directed down- 

 ward and outward. It is the direct antagonist of the in- 

 ferior oblique, the action of which has been described in 

 connection with the motor oculi communis. "When the pa- 

 theticus is paralyzed, the eyeball is immovable, as far as 

 rotation is concerned ; and when the head is moved toward 

 the shoulder, the eye does not rotate to maintain the globe 

 in the same relative position, and we have double vision. 3 



Motor Oculi Externus, or Abducens (Sixth Nerve). 



Like the patheticus, the motor oculi externus is distrib- 

 uted to but a single muscle, the external rectus. Its uses, 

 therefore, are apparent from a study of its properties and 

 distribution. 



Physiological Anatomy. The apparent origin of the 

 sixth nerve is from the groove which separates the anterior 



1 LONGET, Traite de physiologic, Paris, 1869, tome Hi., p. 559. 



8 CHAUVEAU, Recherches physiologiques sur Vorigine apparante el sur VorigvM 

 r&elle des nerfs moteurs craniens. Journal de la physiologic, Paris, 1862, tome v., 

 p. 275. 



8 See page 130. 



