128 PROFESSOR, MARSHALL. 



Now these two points are of primary importance, forming, as is at 

 once seen, the whole basis of Stieda's argument ; and in relying on 

 them he is very far from standing alone. Indeed, until some five or 

 six years ago, their correctness has been assumed, either tacitly or 

 explicitly, by the great majority of those who have dealt with the 

 cpiestion, including some of the most eminent anatomists of the time, 

 such as J. Muller, 1 Arnold, 2 Langer, 8 Gegenbaur, 4 and, though in a 

 somewhat less positive manner, Huxley. 5 I direct attention to this at 

 once, because we shall find further on that there are very strong 

 reasons for holding that neither of the points in question is really 

 correct. I have taken Stieda as the most recent representative of a 

 school to which C. V. Cams, Arnold, Buchner, J. Muller, Langer, 6 and 

 many other prominent anatomists belonged, a school which attacked 

 the problem of the segmental value of the cranial nerves by first 

 determining perfectly independently the number of segments or 

 skull-vertebra) in the head, a determination made as a rule on very 

 insufficient and often purely fanciful grounds, and having thus 

 decided the number of segments, and therefore of segmental nerves, 

 proceeding to apportion the several nerves to these segments, usually 

 in a very arbitrary manner. The writers named above differ, indeed, 

 in the number of head-segments they respectively adopt, but agree in 

 the principle on which they work, viz., determining the number of 

 segmental nerves from that of the supposed segments or vertebral composing 

 the skull. 



Stannius was the first to deal with the question in a more philo- 

 sophical spirit, and to attempt to determine the number of segmental 

 nerves by a direct study of the nerves themselves. The results of his 

 investigations 7 are contained in his invaluable treatise on the Peripheral 

 Nervous System of Fishes published in 1849. He leaves the three 

 nerves of special sense out of consideration for the same reason as 

 Stieda and the other anatomists we have mentioned, i.e. that they 

 are rather parts of the brain than true nerves. Ho also omits the 



1 Joh. Muller, Handbuch der Physiologic des Mcnschen, 1844, p. G31. 



s Arnold, Ilandbuch der Anatomic des Menschen, 1851, Bd. ii. pp. 830-834. 



3 Langer, Lehrbuch der Anatomie des Menschen, 1865, p. 429. 



4 Gegenbaur, " Uber die Kopfnerven von Hexanchus," Jenaiscive Zcitschrijt, Bd. vi. 1871, 

 pp. 548-551. 



6 Huxley, The Anatomy of Vertcbrated Animals, 1871, pp. 71-74. 



An excellent summary of the views of these and other writers on the segmental value 

 of the cranial nerves will be found in Stieda's paper already quoted. They all agree in 

 principle with the account given above, the differences being merely in points of detail. 



» Stannius, Das pcripherische Nervensystem der Fische, Rostock, 1849, pp. 125-131. 



