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position in the interior of the mouth cavity, must first come to lie 

 between the premaxillary bone and the maxillary breathing valve, or 

 between the anlagen of these two structures, and then, advancing 

 further, they must either cut through the anläge of the valve, and 

 hence of the bones related to it, or they must push those bones back- 

 ward, ahead of them, on to the more posterior parts of the roof of 

 the mouth. If the internal nares cut through the anläge of the valve, 

 the valve, afterwards developing normally, but perhaps in three sections, 

 would certainly furBish a structure that might naturally give origin to 

 the secondary palate, which palate would, in fact, have been fore- 

 told by the valve in fishes. If, on the contrary, the internal nares re- 

 main always anterior to the valve, the valve could have nothing to 

 do with the formation of such a palate. 



This utilization of the maxillary breathing valve of fishes to form 

 the secondary palate of the higher animals would fully account for 

 the incorporation of a part of the original mouth cavity in that of the 

 nose, while, without the predetermining valve, it would seem as if the 

 final result attained might have been much more directly arrived at 

 by a simple enlargement of the nasal cavity. But as to whether the 

 valve has been utilized, or not, I find very little indeed, in the lite- 

 rature at my disposal, that warrants an opinion one way or the other. 



In the larvae of certain Urodeles Paeker (No, 29) describes a 

 dentigerous vomer that has strongly the appearance of being the ho- 

 mologue of the maxillary breathing valve bone of Polypterus. The 

 internal nasal aperture of these young urodeles lies external to this 

 bone, between it and a line of fibrous tissue that extends from the 

 hind end of the premaxillary to the quadrate, and that represents the 

 anläge of the maxillary bone of the animal. Later, the dentigerous 

 vomer is pushed out of its larval position and coalesces with the 

 anterior end of the larval palatine bone to form the palatine of the 

 adult. At the same time the anterior end of the pterygoid moves 

 outward toward the hind end of the maxillary, and non-dentigerous 

 vomer plates are developed that apparently are, in origin, wholly in- 

 dependent of the dentigerous ones. This somewhat complicated process 

 receives a fairly reasonable explanation under the assumption that the 

 maxillary of Amphibians is the dermopalatine of fishes, the palatine 

 the entopterygoid, a part of the pterygoid the ectopterygoid, and the 

 larval dentigerous vomer the maxillary breathing- valve bone. This 

 latter bone, which is by origin of a floating character, is then perhaps 

 here being pushed out of its primary relations to the neighbouring 

 parts by the developing internal nasal aperture. In the frog (No, 27), 



