Literary Notices. V 



act after the cerebral hemispheres have been removed, there is no 

 dispute over the fact that such movements are due to the workings of 

 a nervous machine and nothing more." 



We heartily commend the author's emphasis upon the necessity 

 for an out-of-door life and a symmetrical training of all the senses if 

 we would secure the highest educational results ; but Mr. Halleck's 

 system, like his book, is too ill-balanced to be safely followed. 



c. J. H. 



The Morphology of the Optic Nerve. 



The fact that the optic " nerve " is not a nerve at all in the strict 

 sense of the term, but an integral part of the central nervous system 

 is of course now all but universally recognized. Yet its position is in 

 many respects unique and the problems connected with its morpholo- 

 gy and evolution are by no means all happily settled. Thanks to the 

 labors of W. Miiller, KoUiker, Keibel, Cajal and Froriep, among oth- 

 ers, we may now consider it definitely established that the major part 

 of the fibers of the optic nerve arise in the ganglion cells of the retina 

 and grow centrally to terminate in arborizations in the tectum, while 

 there is a reasonable probability that a smaller number of fibers arise 

 in the tectum and pursue the opposite course. Yet one of the more 

 recent contributors to this question^ asserts that in the frog the fibers 

 in growing from the retina to the optic tectum pass, not through the 

 optic stalk, but outside of it. " The optic nerve is developed inde- 

 pendently of the optic stalk, the nerve fibres lying along the posterior 

 border of the stalk, and at first entirely outside it ; but on the break- 

 ing down of the stalk, some of the nerve fibres grow in between the 

 cells." This is equivalent to saying that a tract of fibers in passing 

 from one part of the central nervous system to another takes a paih 

 which for a part of its course lies entirely outside of the system — cer- 

 tainly an improbable condition. In order to test the matter Dr. Ar- 

 thur Robinson has followed the development of the optic nerve in a 

 number of representative mammals. ^ In brief, he confirms the re- 

 sults of the first mentioned authors that the nerve fibers grow inside 

 of the optic stalk and among the cells which constitute its wall. He 



1 AsHETON, R. On the Development of the Optic Nerve of Vertebrates 

 and the Choroidal Fissure of Embryonic Life. Quart. Jour. Micr. Set,, August 

 1892. 



' Robinson, Arthur. On the Formation and Structure of the Optic 

 Nerve and its Relation to the Optic Stalk, /our, of Anat, and Physiol,, XXX, 

 N. S. X, 3, April, 1896. 



