

On the Cranial Nerves of Elasmobranch Fishes. 525 



I have not yet had an opportunity of comparing Lcemargus with 

 either Hexanchus or Echinorhinus, but I have satisfied myself that the 

 accounts given of the cranial nerves of these forms are not applicable 

 in several important respects to the cranial nerves of Lcemargus, nor 

 yet to the nerves of the common skate (Raia batis). Further, I find 

 that when, having mastered the arrangement of the cranial nerves of 

 Lcemargus and Raia, one turns to Petromyzon, Scyllium, Galeus, and 

 other familiar forms, it is impossible to accept many of the statements 

 hitherto made as to the nature, distribution, and segmental value of 

 the cranial nerves of vertebrates. 



In this preliminary communication I propose to describe shortly 

 the cranial nerves of Lcemargus and Raia, reserving for a future 

 paper a comparison between the nerves of Lcemargus and other 

 Elasmobranchs, and the consideration of the segmental value and the 

 more important modifications of the cranial nerves in the chief sub- 

 divisions of the vertebrate group. 



I. The Cranial Nerves of Lsemargus. 



As the olfactory and optic nerves closely resemble those of 

 Hexanchus, it is unnecessary to refer to them in this preliminary note, 

 and instead of beginning, as is usually done, with the oculo-motor, I 

 shall first describe the ophthalmicus profundus. 



1. The Ophthalmicus Profundus. This nerve has usually been said 

 to belong either to the oculo-motor or to the trigeminal. It presents 

 a root, more or less distinct, a root ganglion, and a trunk which gives 

 off a number of well-marked branches. Although the segmental 

 value of the ophthalmicus profundus need not now be discussed, it 

 may be mentioned that since van Wijhe demonstrated that it 

 possessed a ganglion, its right to rank as a separate cranial nerve has 

 been deemed worthy of consideration. Although Marshall and 

 Spencer concluded that there was nothing in support of the view that 

 the root of this nerve belonged to the trigeminal, and believed that its 

 trunk was a branch of the oculo-mobor, Gegenbaur has recently 

 stated that he considers the ophthalmicus profundus with its ganglion 

 as part of the trigeminal. Very different views have been held 

 as to the ganglion of the ophthalmicus profundus. By Marshall 

 and Spencer the ganglion was said to belong to the oculo-motor, 

 and was identified as the ciliary ganglion. Beard, on the other 

 hand, considers the ganglion of the ophthalmicus profundus as 

 homologous with the Gasserian ganglion, while he thinks the ciliary 

 ganglion probably corresponds to a sympathetic ganglion. Believing, 

 with van Wijhe, in the possible existence of two ganglia, one on the 

 ophthalmicus profundus and one (the ciliary) in connexion with the 

 oculo-motor, Beard has given to the ganglion of the ophthalmicus 



