168 EDWARD PHELPS ALLTS, JUN. 



" But there is a very large nerve, a liranch of the tri- 

 o-eminal, which in the Rav arises almost directly from the 

 short common trunk, but is buried up for a short distance 

 with the second division of the fifth, and then passes forwards 

 and inwards along the base of the skull, and on the inner side 

 of the nasal capsule, to the snout, where it divides into a leash 

 of branches for the sensory tubes of that region. From the 

 outer side of this nerve, while it lies in the orbit, branches 

 are given off to the posterior face of the olfactory capsule. 



" This nerve is identiBed by Stannins with what he terms 

 the ramus buccalis of the maxillary nerve in osseous fishes. 

 But it appears to me to have nothing to do with this nerve, 

 which is otherwise represented in the Rays. 



" The branch of the trigeminal under discussion appears 

 to exist in all the Plagiostomes, and considering the many 

 embryonic characters retained by these fishes, I am led to 

 believe that it represents in a distinct form a nerve which in 

 most fishes and in the higher vertebrates has coalesced with 

 the anterior palatine division of the seventh, and has in that 

 manner griven rise to the Videan nerve." This branch of the 

 trigeminus in the Ray is later always referred to by Professor 

 Huxley as the palato-nasal. 



Huxley then states his conclusions : — (1) That the spiracle 

 of the Ray '^ answers to the tympano-Eustachian pnssage of 

 the higher Vertebrata," and (2) ''that the palato-quadrate 

 cartilage in the Ray and other corresponding structures in 

 the embryo of the higher Vertebrates is a mere appendage 

 of the mandibular arch, and not a distinct visceral arch, as I 

 was formerly inclined to suppose." 



He then says : — " But if the pterygoid cartilage is only an 

 outgrowth of the mandibular arch, it follows that the space 

 between the mandibular and the trabecula on each side repre- 

 sents a trabecule-mandibular visceral cleft, and this ought to 

 be supplied by a nerve dividing into anterior and posterior 

 divisions as the portio dura does. It appears to me that there 

 is no difiiculty in finding the posterior division or nerve dis- 

 tributed to the (morphologically) anterior face of the mai:)- 



