ORAL CIRRI OP SILUROIDS AND ORIGIN OF THE HEAD IN VERTEBRATES. 23 



of the mouth of Teleostei. These structures possess no great morpho- 

 logical importance. A similar phenomenon is seen in the nose of 

 Myxine, where a small process forms a partial septum in the nasal tube. 



I propose to deal with the Selachii and some other forms later on. 



In the Sturgeon, the most median of the two pairs of tentacles 

 appears, from its nerve supply, to be the premaxillary tentacle. 



The premaxillary tentacle of Myxine is the one which Miiller showed 

 to be the first, though viewed externally it lies inside and below the 

 morphologically second. It is continuous with the unpaired bar of 

 hard tissue, which underlies the nasal tube, and which is its root piece. 

 Miiller terms this premaxillary block the " knocherne Stiitze der 

 Schnauze," and has given full details. 



Nerve Supply. 



Two nerves supply the region of the premaxilla. They are the 

 palatine and a branch of the maxillaris, which I term here the pre- 

 maxillary. The R. premaxillaris occurs throughout the Siluroids, Avith 

 comparatively unimportant variations. In Auckenaspis it runs along 

 with part of the buccalis. 



The palatine nerve is also present in all Siluroids examined by me. 

 It supplies the muscle which moves the prepalatine piece and, except 

 in Callichthys, proceeds forward to the tip of the snout. 



The R. premaxillaris corresponds to the nerve supplying the pre- 

 maxillary tentacle of Myxine. This is usually considered to be an 

 ophthalmic branch, and I have kept the old name in my preliminary 

 communication, However, it is better to consider it a special branch, 

 and not a mere portion of the ophthalmic. It is said to run over the 

 optic nerve in Bdellostoma, and under it in Myxine, as in other verte- 

 brates. It runs mainly in the substance of the palato-ethmoidalis 

 superficialis muscle (Fiirbringer) the Retractor of the bony support of 

 the snout (Miiller), outside the premaxillary piece, beyond which it 

 gives off a motor branch to one portion of the Depressor of the mouth 

 (U' of Miiller). It then supplies the premaxillary tentacle, which also 

 receives a twig from the ophthalmicus profundus. 



Concerning the R. palatinus there are widely divergent opinions, 

 which have been summarized by Slannius. In Silurus glanis he states 

 that it is undoubtedly a branch of the Trigeminus. In other forms it 



