MUSTELUS LMYIS. 205 



profundus is said to either pierce the rectus superior muscle, 

 or to lie wholly ventral to it, and then to run forward ventral 

 not only to the obliquus superior, as stated by Stannius, but 

 ventral also to the rectus internus. Schwalbe's descriptions 

 and figures also show that the ramus profundus lies between 

 the superior and inferior divisions of the nervus oculomotorius, 

 ventral to the former and dorsal to the latter, but he does not 

 call attention to this important fact. In his references to 

 teleosts and ganoids he makes no application of the terms 

 portio major and portio minor. 



Balfour in his well-known work on the development of 

 elasmobranch fishes, to which I am unable to directly refer, 

 and which was published shortly before Schwalbe's work 

 above referred to, described, according to Marshall and 

 Spencer (43), the ophthalmic nerves both in the adult and in 

 embryos of Scyllium. In those descriptions he is said to 

 have entirely overlooked the true profundus nerve, giving the 

 name ramus ophthalmicus profundus to what Schwalbe 

 describes as the portio minor of the superficial nerve. 

 Balfour, although he Avas thus, as Marshall and Spencer state, 

 the first to clearly recognise the double nature of the super- 

 ficial ophthalmic nerve of elasmobranchs, Avas also probably 

 the first to make that misapplication of the name profundus 

 that has since caused so much confusion in the descriptions 

 and discussions of these nerves. Balfour evidently did not 

 so apply this term either thoughtlessly or carelessly, for 

 Marshall and Spencer state that he sought to explain the 

 apparently exceptional position of the nerve in Scyllium by 

 the assumption that it had shifted upward from the deeper 

 position in which it is usually found in selachians ; this 

 explanation adding, in my opinion, a misconception of the 

 nerves to a misapplication of their names. 



Marshall, in his own embryological work on Scyllium (42), 

 and also in a second work on the same fish published in con- 

 nection with Spencer (43), concluded that the portio major 

 and portio minor of Schwalbe's descriptions were, respec- 

 tively, the ophthalmic branches of the facial and trigeminal 



