vi DIOPTRIC MECHANISM OF THE EYE 317 



The dilatator fibres to the iris start from the ventral roots of 

 flic eighth cervical and first thoracic nerves; they run by the rami 

 commuuicantes to the superior thoracic ganglion, thence to the 

 inferior and superior cervical sympathetic ganglia, and enter into 

 relation with the nerve-cells oi' the latter. The fibres that take 

 origin from these, according to Laugendorff, must be regarded as 

 the peripheral dilatator fibres of the pupil ; they run to the eye 

 from the plexus cavernosus as the long ciliary nerves. From the 

 superior cervical ganglion other dilatator fibres ascend to the 

 Gasserian ganglion, unite with the ramus ophthalmicus of the tri- 

 geminus, and also penetrate the eye as long ciliary nerves, without 

 coming into relation with the ciliary ganglion. 



The results of experiments bear out this course of the motor 

 paths to the iris muscles. Pourfour du Petit (1727) was the first 

 who observed that section of the sympathetic caused contraction 

 of the pupil as well as conjunctival hyperaemia. Biffi (1846) 

 completed the experiment by demonstrating that excitation of 

 the sympathetic produces dilatation of the pupil. Budge (1851-55) 

 discovered the spinal origin of the dilatator fibres of the pupil 

 (Vol. III. p. 352). Claude Bernard (1858) found that the cervical 

 sympathetic contains vaso-constrictor fibres to the iris as well as 

 vaso-dilator fibres ; that the vaso-constrictor fibres separate from 

 the irido-dilatators above the superior cervical ganglion, the first 

 following the course of the carotid, the second uniting into a 

 branch that joins the Gasserian ganglion. On exciting these 

 nerves alternately, Francjois-Franck (1884) obtained vaso-constric- 

 tion and vaso-dilatation in the iris, and found that mydriasis 

 precedes vaso-constriction. Other observations show that the 

 dilatator fibres of the Gasserian ganglion unite with the ramus 

 ophthalmicus, and after section of the latter stimulation of the 

 cervical sympathetic no longer produces mydriasis (Budge, Waller, 

 Bolay, Franc^ois-Franck, and others). Lastly, Braunstein's experi- 

 ments (1894) showed that after extirpating the ciliary ganglion 

 mydriasis could be provoked, either by exciting the cervical 

 sympathetic or by direct stimulation of the long ciliary nerves. 



The irido-con stricter action of the oculo-motor was first pointed 

 out by Herbert Mayo (1823); but it was reserved for Claude 

 Bernard (1858-62) to demonstrate that '' the fibres of the third 

 pair of nerves become active after passing through the ciliary 

 ganglion," and that stimulation of the intracranial branch of the 

 oculo-motor has no effect on the sphincter of the pupil, while 

 stimulation of the short ciliary nerves causes pronounced myosis. 

 Kolliker and Michel (1894-96) found an anatomical connection 

 between the fibres of the oculo-motor and the cells of the ciliary 

 ganglion, from which the constrictor fibres for both the sphincter 

 of the pupil and the ciliary muscle are derived. Apolant (1896) 

 confirmed this, and observed that after section of the third nerves 



