277 



mucous fold turns outward, ventrally to the hind edges of the pre- 

 splenial bones, these bones thus being ossifications of the mandibular 

 valve. The two breathing valves of the fish are thus here probably 

 indicated, and that dermal bones, related to teeth, should develop in 

 them is wholly natural, and it is even foretold in the small, hard 

 eminences found in considerable number on the breathing valves of 

 certain fishes, such for example as the "green bass" of the united 

 States, a specimen of which I happen to have, and have examined. 



VAN WijHE (No. 47, p. 253) says of these maxillary breathing- 

 valve bones of Polypterus that they are functionally dermopalatines, 

 and that Tkaquair's ectopterygoid should be more properly called a 

 dermo -pterygopalatine, thus practically accepting the earlier view of 

 these bones said by Traquair to have been held by MtJLLER. The 

 maxillary breathing-valve bone, however, comes into no relation with 

 the autopalatine, being shut oif from it not only by the ectopterygoid 

 but also by the palatal plate of the maxillary, van Wljhe was thus, 

 in my opinion, right only in so far as that he doubted that the bones 

 were vomers. 



Between the posterior portions of the adjoining mesial edges of 

 the two so-called vomer bones there were, in the 30-cm specimen 

 used for the figures, the only one that was here carefully examined, two 

 small and separate tooth-bearing plates, one on each side of the head. 

 The hind edges of these two little bones form the median portion of 

 the hind edge of the maxillary valve of the fish, being ossifications 

 of that valve as the so-called vomers are. The two bones, together, or 

 the two bones fused with the little overlying dermal plate that lies 

 between the adjoining edges of the palatine processes of the pre- 

 maxillaries, must represent the unpaired subrostral of Pollard's (No. 32) 

 descriptions. This subrostral of Pollard I was inclined to consider, 

 in an earlier work (No. 3, p. 457), as the probable homologue of the 

 vomers of Amia fused with each other. But as I now find that it, 

 or at least the tooth-bearing part of it, is developed in, and as a part of, 

 the breathing valve of the fish, it cannot be the homologue of the vomers 

 of Amia, those bones developing in relation to teeth that lie posterior 

 to the breathing valve of the fish. In Polypterus this position, posterior 

 to the breathing valve, becomes internal to, or dorsal to, it, because of 

 the almost complete coalescence of the valve with the roof of the 

 mouth; the palatal plates of the premaxillaries thus having, in Poly- 

 pterus, the relation to the breathing valve that the vomers have in Amia, 

 and hence doubtless being the homologues of those bones. The sub- 

 rostral may perhaps, nevertheless, be the homologue of the Teleostean 



