400 H- ß- POLLARD, 



has given rise to the views of some embryologists on the paired nature 

 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. Müller terms this premaxillary block the "knöcherne 

 Stütze 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, with 

 comparatively unimportant variations. In Auchenaspis 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 Callichthjs, 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 

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

 superficialis muscle (FCrbringer) the Retractor of the bony support 

 of the snout (Müller), outside the premaxillary piece, beyond which 

 it gives ofl a motor branch to one portion of the Depressor of the 

 mouth (U' of Müller). 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 Stannius. In Silurus glanis he 

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

 forms it appears to be Facial, and finally in "Ganoids", elements of 

 the Glossopharyngeus enter into its composition (v. Wljhe). 



