204 EDWAED PHELPS ALUS, JUN. 



Plag-iostomata one braiicli only of the nerve lias that course^ 

 the other running* forward across the orbit ventral to the 

 rectus superior and obliquus superior muscles ; its relations to 

 the rectus internus not being- especially mentioned. This 

 latter branch of the nerve in the Plagiostomata is called by 

 Stannius the ramus ophthalmicus profundus^ and as he does 

 not apply this term^ profundus, to the deeper one of the two 

 branches in those teleosts in which two ophthalmic branches 

 are said to be found, it seems evident that he intended the 

 term to be limited to a nerve that held a position anatomically 

 different from that of an ophthalmicus superficialis. It seems, 

 however, equally evident that he considered the two strands 

 of the superficial nerve in teleosts as the homologues of the 

 two more completely separated branches in the Plagiostomata. 

 He says that the superficial strand in teleosts, and the ramus 

 superficialis in the Plagiostomata, are both derived from a 

 posterior, broad-fibred root, while the deeper strand in the 

 former, and the ramus profundus in the latter, arise from the 

 anterior trigeminal root. 



Schwalbe (57, p. 182) concluded that the ophthalmicus 

 superficialis of Stannius's descriptions of selachians was formed 

 of two distinct and different components, the larger one of 

 which always lay superficial to the other. He accordingly 

 called the two components the portio major and portio minor 

 of the superficialis nerve, and says that they derive their 

 fibres partly from the dorsal part of the posterior root of the 

 trigeminus, and partly from the anterior, more ventral root of 

 that nerve. These two bundles of fibres he calls the " radix 

 dorsalis (posterior) and ventralis (anterior) ophthalmici." 

 The portio major of the ophthalmic nerve is said to receive 

 all the fibres that traverse the radix dorsalis, and to be com- 

 posed of those fibres alone. The portio minor receives one 

 half of the fibres that traverse the radix ventralis, the other 

 half of those fibres going to form the ramus ophthalmicus 

 profundus. The portio minor and the ramus profundus are 

 thus formed of similar fibres, and those fibres are said to be 

 derived from the anterior root of the trigeminus. The ramus 



