On the Cranial Nerves of Elasmolranch Fishes. 537 



vagus escapes from the cranium, while the fourth (5 6, fig. 2) is 

 united with the intestinal nerve (t, fig. 2) until the level of the fifth 

 branchial cleft is reached. In each of the three anterior branchial 

 nerves the ganglion is situated within a shorb distance of the point of 

 bifurcation into the post- and pre-branchial branches. The ganglion 

 of the fourth nerve lies in contact with the common trunk from 

 which it springs. (3.) The intestinal nerve (i., fig. 2) passes back- 

 wards, and has its ganglion immediately beyond the point where it 

 separates from the last branchial. Sometimes one (1 sp., fig. 2), or 

 two ventral roots of spinal nerves arise under cover of the roots of the 

 vagus and escape through the occipital region of the cranium, but as 

 in Lcemargus they never unite with any of the fibres of the vagus, and 

 there is no reason for considering them as ventral roots of the vagus 

 complex. 



I am indebted to Mr. Sim, naturalist, Aberdeen, for the specimens 

 of Lcemargus required for the investigation. 



The following list includes the more important papers and works 

 referred to : 



Balfour. ' A Monograph of the Development of Elasmobranch Fishes.' 



* Comparative Embryology.' 

 Beard. "Sense Organs of Ichthyopsida," 'Quart. Journ. of Microsc. Science,' 



1885. 

 " The Ciliary and Motor-oculi G-anglion and the G-anglion of the Ophthal- 



micus pro t'undus in Sharks," ' Anat. Anzeiger,' 1887, Nr. 18 19. 

 " The Development of the Peripheral Nervous System of Vertebrates," 



'Quart. Journ. Microsc. Science,' October, 1888. 

 Froriep. ' Anat. Anzeiger,' vol. 2, 1887. 

 Q-arman. " On the Lateral Canal System of Selachia and Holocephala," ' Bulletin 



Mus. Comp. Zool., Cambridge, Mass.,' vol. 17, No. 2. 

 G-askell. " On the Relation between the Structure, Function, and Distribution of 



the Cranial Nerves," ' Roy. Soc. Proc.,' vol. 43. 



Q-egenbaur. " Die Kopfnerven von Hexanchus," ' Jenaische Zeitschrift,' vol. 6. 

 "Die Metamerie des Kopfes und die Wirbeltheorie des Kopfskeletes," 



'Morphol. Jahrb.,' vol. 13. 

 Jackson and Clarke. " The Cranial Nerves of Echinorhinus spiriosus,' ' Journal 



of Anat.,' vol. 10. 

 Krause. " Ueber die Doppelnatur des Ganglion ciliare," ' Morphol. Jahrbuch,' 



vol. 7. 

 Marshall. " On the Cranial Nerves of Scyllium," ' Quart. Journ. Microsc. Science,' 



1881. 



" The Segmental Value of the Cranial Nerves," ' Journal of Anatomy,' vol. 16. 

 Schwalbe. " Das Ganglion oculomotorii," ' Jenaische Zeitschrift,' vol. 13. 

 Stannius. ' Das Peripherische Nervensystem der Fische,' Rostock, 1849. 

 van Wijhe. " Ueber d. Mesodermsegmente, and iiber die Entwicklung der 

 N erven des Selachier-Kopfes," Amsterdam, 1882. 



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