OPHTHALMIC NERVES OF GNATHOSTOME FISHES 77 



strongly suggests this portio. Of this process Landacre says 

 that it '4s evidently the remains of the structure which Neal 

 identifies as a persistent connection of the ganglion with the ec- 

 toderm, ^nd which Scammon identifies as the utrochlea process, 

 i.e., the remains of the connection of this ganglion with the 

 neural crest." 



The conditions in the several fishes above considered thus show 

 that there are two distinctly different nerves that may supply 

 the general cutaneous fibers that are distributed to the dorsal 

 surface of the anterior portion of the head. One of these nerves 

 is the so-called ramus ophthalmicus superficialis trigemini, the 

 other what I have called the ramus ophthalmicus profundi, the 

 frontal branch of the latter nerve being the so-called portio 

 ophthalmici profundi. The trigeminus one of these two nerves 

 always issues from the cranimn posterior to the pedicel of the 

 alisphenoid, or posterior to a corresponding process of the para- 

 sphenoid, while the profundus always issues anterior to that 

 pedicel or process, and I consider these peripheral relations to 

 these structural elements to be as definite and positive evidence 

 of the segments to which the nerves belong as are the facts of 

 development and the central origins of the nerves. 



The relative importance of these two ophthalmic nerves varies 

 greatly in different fishes, as does also the relative importance 

 of the frontal and nasal branches of the ramus ophthalmicus pro- 

 fundi, and it would seem as if the frontal branch alone of the 

 latter nerve might be the serial homologue of the entire ophthal- 

 micus trigemini. In the Selachii, where there is apparently 

 both a ramus ophthalmicus profundi and a ramus ophthalmicus 

 trigemini, the portio ophthalmici profundi is wholly wanting, 

 unless it be represented in some part of the so-called ophthalmicus 

 trigemini. In the Holostei and certain of the Teleostei there 

 is an ophthalmicus trigemini and a portio profundi, but the 

 ramus ophthalmicus profundi, if 'present at all, is a small and 

 degenerate nerve (Amia). In certain others of the Teleostei 

 (Scomber) there is an ophthalmicus trigemini, but neither ramus 

 ophthalmicus profundi nor portio profundi. In Polypterus, and 

 probably also in Ceratodus, there is a ramus ophthalmicus pro- 



