VISION. 



781 



veyed by the optic nerve to the anterior corpora quadrigemina and 

 then to the oculomotor nucleus and by its nerves to the iris. It is not 

 due to the direct action of light upon the iris itself. 



The following cause changes in the diameter of the pupil: 

 Contraction of Pupil. Stimulation of optic nerve; stimulation 

 of third cranial nerve ; section of fifth cranial nerve ; section or 

 paralysis of the cervical sympathetic; light acting on retina; accom- 

 modation for a near object; myotics (eserin, stimulation of the ends 

 of oculomotor); anaesthetics (at first). 



Dilatation of Pupil. Section of the optic nerve; paralysis of 

 third cranial nerve; stimulation of fifth cranial nerve ; stimulation 



Fig. 331. Isolated Lens Fibers. (J. ARNOLD.) 



of sympathetic; stimulation of sensory nerves; mydriatics (atropin, 

 by paralyzing the ends of oculomotor); dyspnoea, asphyxia; anaes- 

 thetics (at the end). 



Meltzer and Auer have shown that, with the superior cervical 

 ganglion present, adrenalin does not act on the pupil. When the 

 ganglion is removed, then adrenalin dilates the pupil. I have con- 

 firmed this statement. 



THE CRYSTALLINE LENS. The lens is situated behind the iris, 

 and enclosed in a distinct capsule. The lens consists, in the begin- 

 ning, of cylindrical cells, which in the course of development in- 

 crease in height, until exceedingly long cells are formed. The lens- 

 fibers are flattened hexagonal prisms, which are thickened at their 

 posterior ends. They run in a meridional direction from the an- 



