410 H- B- POLLARD, 



of Crossopterygia may have arisen. On my view the jugular plates 

 would, like the premaxillae and maxillae, arise in connection with 

 tentacles. However direct evidence is still wanting, unless indeed 

 certain phenomena in Ceratodus may be interpreted as such. Huxley 

 has described an eusheathing bone at each side of the symphysis, on 

 the ventral face of the mandible. This he takes to be the dentary 

 element, setting aside Günthers determination of the tooth as the 

 dentary. The bone in question however lies in front of and below 

 the mental cartilage, and may be interpreted on Gegenbaur's sug- 

 gestion, as a paired anterior jugular plate. Jugular plates occurred 

 in fossil Dipnoi but are usually stated to be absent in the living forms 

 (Smith Woodward). This bone is absent in Protopterus. 



The mental tentacle in Myxinoids is represented by a hard root- 

 piece, bearing a rudimentary tentacle and suspended only by ligaments 

 and muscles. It is fully described by Müller as the cartilage in the 

 4''' or lowest tentacle. 



Nerve Supply. 



The nerve supply of the mental region is from the R. mentalis 

 and the R. mandibularis externus. The Ramus mentalis in Siluroids 

 runs outside or above the mentomeckelian process and forward, to 

 run down outside the tentacle, where that is present, or to branch in the 

 skin, when the tentacle is absent. The Ramus mandibularis externus 

 may be a dissociated branch of the R. mentalis. It runs outside the 

 coronoid process supplying in Auchenaspis the fold of skin below the 

 mental block of cartilage. In Callichthys it is placed not so far 

 forward. 



Other details are given by Stannius. 



In Misgurnus fossilis, the mental tentacle is supplied by a 

 R. mentalis which crosses the MeckeUan cartilage and then runs below 

 that cartilage. 



In Motella tricirrata the unpaired mental tentacle is supplied by 

 a R. mentalis which takes a shghtly ditl'erent course. It crosses the 

 lower jaw rather far back, and then ])roceeds along with the R. mandi- 

 bularis of the Facial , which supplies the mandibular branch of the 

 lateral line system. This close apposition led Zincone to the erroneous 

 view that the mental tentacle was sui)plied from the Hyomandibular 

 nerve of the Facial. 



The mental tentacle in Myxine is supplied by a mental branch 

 proceeding forward as in Siluroids. 



