NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 273 
lateral, or ventral indicates that the point of view of morphologists 
is now fundamentally different from that of the older anatomists, who, 
in dealing with the question of the segmental value of cranial nerves, 
excluded the eye-muscle nerves from consideration on the ground of 
their inconstancy in appearance and distribution. Except on the part 
of Froriep, Kastschenko, and Rabl, who regard the pre-otic region as 
one sui generis, I find no tendency to revert to the view of Stannius 
(49, p. 125) that “der Parallelisirung der Augenmuskelnerven mit 
Spinalnerven stellen sich, wegen ihrer eigenthümlichen Ursprungs- 
verhältnisse, des ihnen zukommenden Mangels von Ganglien und der 
ausschliesslichen Vertheilung ihrer ungemischten Primitivröhren in den, 
auch ihrerseits mit Muskeln der Wirbelsäule durchaus nicht vergleich- 
baren, Muskeln eines Sinnes-Apparates so unüberwindliche Schwierig- 
keiten entgegen, dass von einer solchen nicht füglich die Rede sein 
kann.” However, the labors of comparative anatomists, among whom 
may be named Huxley, Gegenbaur, M. Fürbringer, and Schwalbe, during 
the thirty years following the work of Stannius just quoted, resulted 
in so well establishing the “ Bürgerrecht” of the eye-muscle nerves 
that morphologists now assume that they are comparable with either 
dorsal or else ventral segmental nerves. Only a minority of anatom- 
ists, among whom may be named Schneider (79), van Wijhe (82), 
Beard (’85), His (’88"), Dohrn (91), Neal (96), and M. Fiirbringer (’97), 
have regarded them as ventral segmental nerves. The weightiest well 
established evidence in favor of this view was first stated by His (88), 
and consists in the fact that the eye-muscle nerves, at least of the adult, 
resemble ventral spinal nerves both in histological structure and in the 
situation of their motor nucleus in the ventral horn of the neural tube ; 
and also in the less well established fact that they innervate muscula- 
ture derived from segments of the dorsal mesoderm. On the other 
hand, the majority of morphologists, among whom may be named Bal- 
four (78), Marshall (81), Dohrn (85, ?87, ’90), Gaskell (89), Hoff 
mann (89, 94), Oppel (220), Houssay C90), Platt (91), Froriep (91), 
Zimmermann (91), Hatschek (92), Mitrophanow (92, '93), and Kupffer 
(94, ’95, ’96), while in general of the opinion that the abducens is the 
homologue of one or more segmental ventral nerves, have held that 
cither the trochlearis or the oculomotorius, or both, represent dorsal (or 
lateral) segmental nerves. The chief arguments in favor of this view 
consist in evidence (1) of the development of these nerves from neural- 
crest cells; (2) of a cellular or so called ganglionic structure of the 
nerves in the embryo ; (3) of transitory or permanent ganglia in con- 
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