NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 227 



regarded as from the earliest stages of develoijment a fibrillar nerve 

 formed bj 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 oculoraotorius in 

 Selachii. I was at first disposed to consider as of some morjjhological 

 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 furnishes us with evidence of a primitive rela- 

 tion of the ramus opthalmicus profundus with this somite (Plate 8, Fig. 

 61). The observations of J. Miiller in 1840, P. Fiirbringer (75), Price 

 ('96), and Max Fiirbringer ('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 ram.) the relations of the trigeminus 

 are unchanged (compare Plate 4, Fig. 19). The r. ophthalmicus pi'o- 

 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 trunk of the nerve are distinctly peripheral in i-elation 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 VII (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 A'^II (incorrectly called supramaxillaris V by 

 "Wiedersheim), developing along the medic-lateral line of the head. 



1 AUis ('97, 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 (III and IV), regards 

 this nerve as homologous with the ophthalmicus profundus trigemini. 



