l8o ALUS. [Vol. XVIII. 



p. 491) that in Nccturus it splits off from a primitive supraorbital 

 ridge of thickened ectoderm, the supraorbital sense organs and 

 the ophthalmicus superficialis developing in and from a secondary 

 ridge which occupies exactly the position of the primitive one. 

 In my work on the cranial nerves of Aniia, I assumed (No. 4, p. 

 635) that the profundus nerve of Necturus, as described in Piatt's 

 earlier work (No. 54), must, from its manner of development, 

 be the homologue of the ophthalmicus superficialis trigemini of 

 Amia. In this I seem to have been wrong, the nerve, as described 

 in her later work, seeming to be, unquestionably, the homologue 

 of the similarly named nerve in other Ichthyopsida, wliere it lies, 

 in the adult, ventral to the rectus superior and obliquus superior 

 muscles, and probably always ventral also to the nerves that inner- 

 vate those muscles. In marked contradistinction to this position 

 in the adult, the nerve must, at the time of its origin from the 

 supraorbital ectodermal ridge, if Piatt is correct, lie dorsal to both 

 those muscles and to the nerves innervating them. Its position 

 in the adult, ventral to these structures, thus needs some special 

 explanation, and this explanation would necessarily differ accord- 

 ing as one assumes that all or certain of the nerves concerned are 

 first laid down as lines of cells, or that they grow peripherally 

 either from the brain or from their ganglia. Relative differences 

 in the times of development of the several nerves might sufficiently 

 account for it, and, as applied to the profundus nerve, developed 

 in the manner stated by Piatt, might also account for the throwing 

 down of certain lateral sensory fibers with that nerve in certain 

 animals and not in others. The simultaneous throwing down of 

 lateral and general sensory fibers seems even to have been observed 

 by Piatt, along the infraorbital line of Necturus, where, according 

 to her (No. 55, p. 520), the infraorbital ridge gives rise to a single 

 nerve " from which the inner part splits off as a trigeminal branch, 

 while the outer part remains as a branch of the facialis." 



In Amhystoma, if I interpret rightly Herrick's figures (No. 35), 

 the ramus ophthalmicus trigemini, which must be the homologue 

 of Piatt's ophthalmicus profundus and of the ramus nasalis of 

 other authors, lies ventral to the nervus opticus. The nerve is 

 said by Herrick to contribute certain fibers to the nervus adducens, 

 destined to innervate the M. retractor bulbi, and certain of its 



