NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 227 
regarded as from the earliest stages of development a fibrillar nerve 
formed by axis-cylinder processes of medullary cells, and that it is no 
more to be regarded as a cellular process or cellular nerve in its earlier 
than in its later stages. The unfavorableness for purposes of nerve 
study of material killed, with the fixing agents commonly used, has 
been the chief cause which has kept us so long from the true under- 
standing of the method of the development of the oculomotorius in 
Selachii. I was at first disposed to consider as of some morphological 
importance the fact that in stages of development before the appearance 
of the oculomotorius a process extends from the mesocephalic ganglion 
to the premandibular somite (Plate 8, Fig. 61). Its earlier appearance 
precluding the view that this process has connection with the oculomo- 
torius, I concluded that it furni ‚hes us with evidence of a primitive rela- 
tion of the ramus opthalmicus brofundus with this somite (Plate 8, Fig. 
61). The observations of J. Muller in 1840, P. Fürbringer (’75), Price 
(96), and Max Fürbringer (’97), have established that this nerve possesses 
motor fibres in the Myxinoids, confirming van Wijhe’s view of its segmental 
value. I am, however, not inclined to lay stress on the fact mentioned 
above as confirmatory of this view, since in later stages (65 somites) I 
also find a similar process, apparently in connection with the “anterior 
cavity ” (Plate 4, Fig. 19).* 
At a stage with 65 somites (10 mm.) the relations of the trigeminus 
are unchanged (compare Plate 4, Fig. 19). The r. ophthalmicus pro- 
fundus trigemini is well differentiated, and shows a marked fibrillar struc- 
ture, especially clear in embryos killed with vom Rath’s fluid. ‘The nuclei 
seen along the truuk of the nerve are distinctly peripheral in relation to 
the nerve fibres. The facialis nerve (VII) now possesses four branches, 
viz. the sensor acusticus branch, connected with the median and ventral 
side of the otic capsule; the mixed hyoid nerve, innervating the muscles 
and skin of the 2d visceral (hyoid) arch; the r. ophthalmicus superfi- 
cialis VIT (ophthalmic branch of the 2d trigeminal root of older anato- 
mists), whose sensor fibres develop in close connection with the skin 
along what in the head corresponds with the dorso-lateral line of the 
trunk; and the r. buccalis VII (incorrectly called supramaxillaris V by 
Wiedersheim), developing along the medio-lateral line of the head. 
1 Allis (797, p. 742) also describes in Amia calva a small and apparently degen- 
erating nerve in connection with the ganglion of the profundus. He however, on 
grounds of the topographical relation of the eye-muscle nerves (IIhand IV), regards 
this nerve as homologous with the ophthalmicus profundus trigemini. 
