BRANCHES AND CONNECTIONS OF THE TRIGEMINUS. 593 



with the ophthalmic division of the trigeminus (Wegner). The iris and retina 

 receive most of their vaso-motor nerves from the trigeminus itself (Rogow), and few 

 from the sympathetic ; according to Klein and Svetlin, the retinal vessels are not 

 influenced either by stimulation or division of the sympathetic. 



4. Motor fibres for the dilator pupillte, which for the most part are derived from 

 the sympathetic (Petit, 1727), through the sympathetic root of the ganglion, and the 

 anastomosis of the sympathetic with the trigeminus (Balogh, Oehl). Some observers 

 deny altogether the existence of a dilator pupillse muscle ( 384). The ophthalmic 

 division contains independent fibres for the dilatation of the pupil (Schif), which 

 arise in the medulla oblongata and proceed directly into the ophthalmic (1 or arise 

 from the Gasserian ganglion Oehl). 



It is not conclusively determined whether in man dilator fibres also proceed through the 

 sympathetic root of the ciliary ganglion, and reach the iris through the ciliary nerves. In the 

 dog and cat these fibres do not pass through the ciliary ganglion, but go directly along the 

 optic nerve to the eye {Hensen and Volckers) through the Gasserian ganglion, to its ophthalmic 

 branch and through the long ciliary nerves {Jegorow). In birds, the dilator fibres run only in 

 the fifth {ZeglinsH). For the centre (367, 8). 



After section of the trigeminus, the pupil becomes contracted after a short period 

 of dilatation (rabbit, frog), but this effect is not permanent. After excision of the 

 superior cervical ganglion of the sympathetic, the power of dilatation of the pupil 

 is not completely abolished. The narrowing of the pupil which follows section of 

 the trigeminus in the rabbit, and which rarely lasts more than half an hour, may 

 be regarded as due to a reflex stimulation of the oculomotorius fibres of the 

 sphincter, in consequence of the painful stimulation caused by section of the 

 trigeminus. 



Stimulation of the Sympathetic. Either in the neck, or in its course to the eye, when the 

 peripheral end of the cervical sympathetic is stimulated, besides the effect on the blood-vessels, 

 there is dilatation of the pupil, as well as contraction of the smooth muscular fibres in the orbit 

 and eyelids. The membrana orbitalis, which separates the orbit from the temporal fossa in 

 animals, contains numerous smooth muscular fibres {muscular orbitalis). The corresponding 

 membrane of the inferior orbital fissure [spheno-maxillary fissure] in man has a layer of smooth 

 muscle, one millimetre thick, and arranged for the most part longitudinally. Both eyelids 

 contain smooth muscular fibres which serve to close them; in the upper lid they lie as if they 

 were a continuation of the levator palpebral superioris, in the lower lid they lie close under the 

 conjunctiva. Tenon's capsule also contains smooth muscular fibres. The sympathetic nerve 

 supplies all these muscles {Heinr. Miiller) (the orbital muscle is partly supplied from the 

 spheno-palatine ganglion) ; in animals, the retractor of the third eyelid at the inner angle of the 

 eye is similarly supplied. Hence, stimulation of the sympathetic causes dilatation of the pupil 

 and of the palpebral fissure, with protrusion of the eyeball. This result may be caused reflexly 

 by strong stimulation of sensory nerves. Strong stimulation of the nerves of the sexual organs 

 is followed by similar phenomena in the eye. The dilatation of the pupil, which occurs in chil- 

 dren affected with intestinal worms, is perhaps an analogous phenomenon. The pupil is dilated 

 when the spinal cord is stimulated (at the origin of the sympathetic), as in tetanus. 



Section of the sympathetic, besides other effects, causes narrowing of the fissure between the 

 eyelids, the eyeball sinks in its socket (and in animals, the third eyelid is relaxed and pro- 

 truded). In dogs, section causes internal squint, as the external rectus receives some motor 

 fibres from the sympathetic. (Origin of these fibres from the cilio-spinal region. Spinal Cord, 

 362,1.) 



5. It is probable that trophic fibres occur in the trigeminus, and pass through 

 the ciliary nerves to reach the eye. If the trigeminus be divided within the 

 cranium, after six to eight days, inflammation, necrosis of the cornea, and ulti- 

 mately complete destruction of the eyeball take place, constituting panophthalmia 

 (Fodera, 1823 ; Magendie). 



Trophic Fibres. In weighing the evidence for and against the existence of trophic fibres, we 

 must bear in mind the following considerations : 1. Section of the trigeminus makes the 

 whole eye insensible ; the animal is therefore unconscious of direct injury to its eye, and can- 

 not therefore remove any offending body. Dust or mucus, which may adhere to the eye, is no 

 longer removed by the reflex closing of the eyelids ; while, owing to the absence of the reflex, 

 the eye is more open and is therefore subject to more injuries ; the reflex secretion of tears is 

 also -arrested. Snellen (1857) fixed the ear of a rabbit in front of its eye so as to protect the 



2 P 



