394 TRACING OF IMPULSES. 



fibers from the nucleus funiculi cuneafi and the descending anterior 

 cerebello-spinal tract. 



Pupillary Reflexes. Pupillary dilatation belongs to the cerebro- 

 spinal group of reflexes. The cilio-spinal center is in the cervical 

 enlargement of the spinal cord. It receives optic impulses through 

 the anterior longitudinal bundle from the corpora quadrigemina. 

 The superior quadrigeminal colliculi receive those impulses by 

 two routes: First, directly, through the fibers of the lateral root 

 of the optic tract, and, second, indirectly, through corticifugal 

 fibers in the occipito- thalamic radiation, and the brachium supe- 

 rius. By the latter route, the optic impulses which have reached 

 the visual area of the occipital lobe, by way of the intrinsic retinal 

 neurones and the optic nerves, tracts and radiation, are returned 

 to the lateral geniculate and superior quadrigeminal bodies. 

 Thence, reaching the cilio-spinal center through the anterior 

 longitudinal bundle, the impulses take the following course: 

 They leave the spinal cord through the anterior roots of the upper 

 thoracic nerves and run, in succession, through the rami communi- 

 cantes, the cervical cord of the sympathetic, the cavernous plexus, 

 the ciliary ganglion and the short ciliary nerves to the radiating 

 fibers of the iris, causing dilatation of the pupil. 



For pupillary constriction, the impulses run directly from the 

 superior quadrigeminal colliculus to the oculomotor nucleus, 

 traversing the anterior longitudinal bundle only through the 

 dorsal tegmental decussation (Meynerti). Then, through the 

 third and short ciliary nerves, they reach the sphincter pupillse 

 muscle. 



