BASE OP BHAIN, OPTIC NEEVE, AND COEPOKA QUADEIGEMINA. 287 



the adult human brain. According to- J. Stilling, there is added still another root 

 which ascends in the pes pedunouli from the medulla oblongata. 



However, it is so difficult correctly to locate and trace out all these libers and 

 nuclei in man that we must ask ourselves the question: How far are the relations 

 under discussion supported by investigations on other vertebrates? First of all, 

 comparative anatomy presents us optic centers of such magnitude in the midbrain 

 of fishes and birds that the relations may be studied there much more easily than in 

 mammals. But in the reptiles and amphibians, as well as in fishes and birds, it is 

 easily recognized that the principal part of the optic nerve certainly ends in the 

 anterior corpus quadrigeminum, and that in its course past the corpus geniculatum 

 laterale it sends numerous collaterals into this ganglion. Experimental investiga- 

 tions (Gudden, Ganser, Monakoiv) on mammals show that after the early extirpa- 

 tion of an eye the anterior corpus quadrigeminum, certain layers of the corpus gen- 

 iculatum laterale, and fibers from the pulvinar degenerate. The pulvinar is, more- 

 over, very small in most mammals, and first attains a considerable size in the 

 Primates. 



It is already evident from the foregoing that numerous methods of investiga- 

 tion have been made use of in order to ascertain the course and termination of the 

 fiber-system of the optic nerve. I have purposely communicated this to you some- 

 what more thoroughly because the history of our knowledge here shows how much 

 is to be gained by the application of many methods to a single object; and, more- 

 over, because I still have something to say concerning new advances which, accruing 

 from the purposive application of the method of degeneration and supported by the 

 results of embryological research, give very important information concerning the 

 combination, and the histology of the termination, of the optic-nerve fibers. 



As you know, only those fibers degenerate which are separated from the cells 

 from which they originate. According as the optic nerve is destroyed at its eye (or 

 peripheral) end or is injured at its terminal points (or centers) very different types of 

 degeneration are obtained. The study of such varied preparations has led Monakow 

 to the conclusion that the majority of the fibers of the optic nerve do not originate 

 from the cells of the brain at all, but from the large ganglionic cells of the retina. 

 The neuraxons that arise there pass backward in the opticus, and in man end for 

 the most part in the corpus geniculatum laterale and in the pulvinar — probably in 

 a brush-like arborization around the cells situated there. The white lines which 

 traverse the gray matter of the lateral geniculate body consist, in part, of such 

 fibers which come directly from the retina. In fact, P. and 8. Bamdn y Cajal have 

 been able to show such brush-like arborizations of the optic fibers terminating around 

 cells in the roof of the midbrain and around cells in the corpus geniculatum laterale, 

 for vertebrates of all classes (see Figs. 66 and 81 also). 



There are fibers, however, in the opticus which originate from the train. 

 From the cells that lie in the superficial gray layer of the anterior corpora quad- 

 rigemina optic fibers certainly arise in the rabbit and cat, and very probably in man, 

 which then go to the retina, and there probably terminate in an arborization around 

 the cells of the granular layer. The optic nerve contains fibers, therefore, which arise 

 from the retina and others that arise from the primary optic centers. Embryo- 

 logical studies by Keiiel and His have shown that certain of the optic fibers grow 

 toward the brain from the large cells of the retina. 



WTiile the existence of the opticus ro.ots asserted to come from the 

 corpus subthalamicum and from the crus cerebri has not as yet been suifi- 



