458 THE NERVOUS SYSTEM. 



different degrees of obliquity to the two eyes, producing uncertainty 

 and double vision. 



The apparent origin of the patheticus nerve is immediately behind 

 the tubercula quadrigemina, on the upper surface of the valve of 

 Vieussens, a thin lamina of white substance, covering the anterior part 

 of the fourth ventricle. The root fibres of the nerve, however, can be 

 traced transversely through the substance of the valve. According to 

 Henle and Meynert, a great part cross the median line, decussating 

 with those from the corresponding nerve on the opposite side ; then, 

 turning downward and forward, they reach a collection of gray matter 

 just behind the nucleus of the oculomotorius nerve, and continuous 

 with it. According to Henle, a portion of the fibres also terminate, 

 without crossing the median line, in the nucleus of the same side. The 

 nucleus is situated beneath the aqueduct of Sylvius and the anterior 

 tubercula quadrigemina ; while the point of exit of the nerve is above 

 the aqueduct of Sylvius and behind the posterior tubercula quadri- 

 gemina. Its root fibres, accordingly, after leaving their nucleus of 

 origin, encircle the walls of the aqueduct, running obliquely upward 

 and backward, and then crossing the median line to their emergence 

 on the opposite side. 



From this point, the nerve passes forward, as a slender filament, not 

 more than one millimetre in diameter, along the upper wall of the 

 cavernous sinus, where it lies in immediate proximity to the oculo- 

 motorius ; and thence, entering the cavity of the orbit by the sphenoidal 

 fissure, terminates in the superior oblique muscle of the eyeball. 



The course of the oculomotorius and patheticus, when compared, 

 shows a remarkable relation between the two nerves. Their fibres 

 originate from adjacent portions of the same nucleus. Those of 

 the oculomotorius pass downward and forward, to emerge from the 

 inner border of the crus cerebri, at the base of the brain ; while those 

 of the patheticus pass upward and backward, emerging from the valve 

 of Yieussens, between the cerebrum and cerebellum. But the nerves 

 afterward run side by side, in their passage toward the orbit, and are 

 finally distributed to muscles associated in the movements of the same 

 organ. 



Physiological Properties of the Patheticus Nerve. The distribution 

 of this nerve to a muscle which receives filaments from no other source 

 indicates in great measure its motor character, which is furthermore 

 established by the results of observation. The experiments of Chau- 

 veau on the horse and rabbit, and those of Longet on the horse, ox, 

 and dog, show that galvanization of this nerve within the cranium 

 produces contraction of the superior oblique muscle, with rotation of 

 the eyeball on its longitudinal axis from without inward ; and in those 

 of Longet there was also a deviation of the pupil outward. In cases 

 quoted by Longet, attributed to paralysis of this nerve, in man, there 

 was incapacity of rotation of the eyeball on the affected side, and con- 

 sequently double vision, the image perceived by the affected eye being 



