TRIGEMINAL NERVE. 685 



root and the connection of the sympathetic with the first division. The 

 iris and the retina probably receive the larger number of vasomotor 

 fibers from the trigemimis itself, and a small number from the sym- 

 pathetic. According to Klein and Svetlin, the retinal vessels are not at 

 all influenced through the sympathetic. 



4. Motor fibers for the dilator muscle of the pupil, which are derived 

 in largest part from the sympathetic, particularly the sympathetic root 

 of the ganglion, and from the anastomosis of the sympathetic with the 

 trigeminus. The first division itself, however, also contains pupil- 

 dilating fibers, passing directly from the medulla oblongata into the 

 first branch. 



After division of the trigeminus the pupil in the rabbit and the frog, 

 therefore, contracts after a brief antecedent period of dilatation ; and after 

 destruction of the superior cervical ganglion of the sympathetic the power 

 of the pupil to dilate is not wholly abolished. The contraction that 

 disappears in the course of half an hour in the rabbit can be looked upon 

 as caused by reflex stimulation of the oculomotor fibers of the sphincter, 

 in consequence of the painful irritation attending division of the tri- 

 geminus. 



Whether dilator-branches pass in man through the sympathetic root of the 

 ciliary ganglion and further on through the ciliary nerves has not been demon- 

 strated with certainty. In the dog and in the cat at least, these fibers do not 

 pass through the ciliary ganglion, but directly along the optic nerve to the eye, 

 all passing through the Gasserian ganglion, the first division and finally through 

 the long ciliary nerves. The center for the motor fibers of the dilator of the pupil 

 is described on p. 749. 



The phenomena brought about by irritation or paralysis of the cervical sym- 

 pathetic or its path upward to the eye may be discussed now. Irritation causes, 

 in addition to dilatation of the pupil, also an effect upon the unstriated muscle 

 in the orbit and the eyelids. The orbital membrane, which separates the orbit 

 from the temporal fossa in animals, contains numerous unstriated muscle-fibers 

 (orbital muscle). The corresponding membrane of the spheno-maxillary fis- 

 sure in man is also provided with a muscular layer i mm. thick, generally passing in 

 a longitudinal direction through the fissure. Further, both eyelids contain un- 

 striated muscle-fibers, which cause narrowing of the palpebral fissure. In the 

 upper lid they continue as a prolongation of the elevator of the upper lid, in the 

 lower they lie just beneath the conjunctiva. Also the capsule of Tenon contains 

 unstriated muscle-fibers. All of these muscles are innervated by the sympathetic 

 (the orbital muscle in part from the spheno-palatine ganglion), as is also the re- 

 tractor of the third eyelid at the inner canthus of the eye in some animals. Irritation 

 of the sympathetic therefore causes dilatation of the pupil, enlargement of the 

 palpebral fissure, and protrusion of the eyeball. This irritation may also be in- 

 duced reflexly by intense stimulation of sensory nerves. Also active stimulation of 

 the nerves of the sexual organs gives rise to the signs 'mentioned in the eye in 

 moderate degree as an accompanying manifestation. Perhaps the dilatation of 

 the pupils in small children in connection with the presence of intestinal irritation 

 from worms also belongs in this category. Also irritation of the spinal cord 

 (sympathetic origin) in cases of tetanus causes dilatation of the pupils. Division 

 of the sympathetic causes narrowing of the palpebral fissure and permits retraction 

 of the eyeball (and projection of the relaxed third eyelid in animals) . The division 

 causes in dogs internal strabismus because the external rectus muscle receives 

 in part motor fibers from the sympathetic. The origin of these fibers from the 

 cilio-spinal region is described on p. 734. 



5. It is as yet undetermined whether trophic fibers also arise from 

 the trigeminus through the ciliary nerves. If the trigeminus be divided 

 in the cranial cavity, there result in the course of from six to eight 

 days inflammation, necrosis of the cornea, and finally destruction of the 

 eveball. 



