500 



NERVOUS SYSTEM 



the decussation of the roots of the third. From this origin, the patheti- 

 cus passes into the orbit by the sphenoidal fissure and is distributed to 

 the superior oblique muscle of the eyeball. In the cavernous sinus it 

 receives branches of communication from the ophthalmic branch of the 

 fifth, but these are not closely united with the nerve. A small branch 

 passes into the tentorium, and one joins the lachrymal nerve, these, 

 however, being exclusively sensory and coming from the ophthalmic 



branch of the fifth. It also receives a 

 few filaments from ,the sympathetic. 



Properties and Uses of the Patheti- 

 cus. Direct observations on the pa- 

 theticus in living animals have shown 

 that it is motor and its stimulation 

 excites contraction of the superior 

 oblique muscle only. 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 over the pulley, 

 where it makes a sharp curve, passes 

 outward and slightly backward and 

 becomes spread out to be attached to 

 the globe at the superior and external 

 part of its posterior hemisphere. It 

 acts on the eyeball from the pulley at the upper and inner portion of the 

 orbit as the fixed point and rotates the eye on an oblique horizontal axis, 

 from below upward, from without inward and from behind forward. 

 By its action the pupil is directed downward and outward. It is the 

 antagonist of the inferior oblique, the action of which has been de- 

 scribed in connection with the motor oculi communis. When the 

 patheticus is paralyzed, the eyeball is immovable so far as rotation is 

 concerned. When the head is moved toward the shoulder, the eye does 

 not rotate to maintain the globe in the same relative position and there 

 is double vision. 



Paralysis confined to the fourth nerve in the human subject is rather 

 unusual. " In seventy-seven cases of paralysis of a single oculomotor 

 nerve I found the third nerve affected in thirty-one cases, the fourth in 

 nine, and the sixth in thirty-seven." (Nettleship.) 



Fig. 119. Distribution of the patheticus 

 (Hirschfeld). 



I, olfactory nerve; II, optic nerves; III, 

 motor oculi communis; IV ', patheticus, by the 

 side of the ophthalmic branch of the fifth, and 

 passing to the superior oblique muscle; IV, 

 motor oculi extern us ; I, ganglion of Gasser; 

 2 . 3. 4. 5. 6. 7, 8, 9, 10, ophthalmic division of 

 the fifth nerve, with its branches. 



