208 EDWABD PHELPS ALLTS, JDN. 



superficialiR, and there fused completely with the portio 

 minor of the ramus superficialis. Such an ascent of the pro- 

 fundus nerve is^ I believe, very generally assumed to have 

 taken place in all teleosts and in most ganoids. In Amphibia 

 and the higher animals it is, on the contrary, as generally 

 assumed that the portio minor of the superficial nerve has 

 moved downward and fused with the ramus profundus. 

 Wiedersheim (64, p. 285) so definitely asserts, and Strong 

 (60, p. 193) accepts as probably correct, a similar statement 

 attributed to Wilder in a work I have not at my disposal. 

 Balfour also definitely accepted this principle in his statement, 

 already referred to, that the profundus nerve of Scyllium had 

 shifted upward to the position of a portio minor of the 

 ophthalmicus superficialis. 



The assumed ascent of one, or descent of the other, of 

 these two ophthalmic nerves seems usually to be made in the 

 sense of a simple juxtaposition and subsequent fusion of the 

 two already developed nerves, but it is evident that this 

 could not take place without the enclosing of the trochlearis 

 and the superior division of the oculomotorius in the single 

 nerve so formed. While this might be assumed, from exist- 

 ing descriptions, to have taken place in certain fishes and 

 other animals, my work leads me to believe that in every such 

 instance it will be found that the motor nerves are simply 

 juxtaposited to one or the other of the two ophthalmic nerves, 

 and not enclosed between the two nerves united. An appa- 

 rent exception to this might be considered as being presented 

 in a single specimen of Carcharias that I examined (5). In 

 that specimen a jDart of the trochlearis certainly perforated 

 and traversed the ophthalmicus superficialis. An important 

 and apparently normal ophthalmicus profundus was, however, 

 found, in this same specimen, in its typical place and relations 

 to the other nerves and structures of the orbit. It might, 

 nevertheless, be said that this perforation of the superficial 

 nerve by a part of the trochlearis here represented some 

 intermediate stage- in the fusion of the superficialis and pro- 

 fundus nerves. This I do not believe, and while the condition 



