285 



the preseuce of the long posterior process of the premaxillary in Am- 

 phiuma (No. 45, Fig. 9). The development of these several bones must, 

 however, be fully known before the homologies of the parts here con- 

 cerned can be definitely settled. 



In Echidna the palate plate is said by Seydel (No. 42) to be 

 formed, not by the anterior, inturned end of the fronto-nasal process, 

 but by horizontal processes that develop mesially from the ventral edge 

 of the maxillary processes of the animal ; and this is the origin usually 

 ascribed to the secondary palate of mammals. The palate plate of 

 Echidna would, accordingly, necessarily present considerable difference 

 to that of the Gymnophionae, if they are both developed from the 

 breathing valve of the animal. The breathing valve of all vertebrates 

 above fishes, if it persists, must, in fact, as the internal nostrils tra- 

 verse it, be cut into three portions, a median one and two lateral ones, 

 and it is the two lateral ones that, in Echidna, by coalescing in the 

 middle line, form much the larger part of the palate plate of the 

 animal, while in the Gymnophionae it is the middle part of the valve 

 that forms the larger part of the palate. The middle, or premaxillary, 

 section of the valve of Echidna, apparently rises, in part, and at a 

 later stage, to the level of the maxillary part of the secondary palate, 

 and there both closes the "Gaumenloch" and gives origin to the pa- 

 pilla palatina. The little piece of cartilage sometimes found in this 

 papilla (No. 42, p. 470) would then be the homologue of the little 

 blocks associated with the velum of Siluroids. 



The fact that the palatine plate of the superior maxillary bone 

 of mammals ossifies from a center distinct and separate from that of 

 the maxillary bone itself (No. 43), has an important bearing on this 

 question; and it receives a natural explanation if the palate plate of 

 mammals be represented in lower animals by a wholly separate and 

 independent bone. 



The maxillary breathing valve of Amia, it may here be mentioned, 

 is a relatively late development, not appearing until the fish is from 

 35 cm to 40 cm in length, thus agreeing, in this, with the relatively 

 late development of the palate plate in higher vertebrates. 



In an earlier work (No. 3, p. 458) I came to the conclusion that 

 the vomer bones of Amia and Teleosts must be the homologues of 

 the palatine process of the premaxillary bone of mammals. 1 since 

 find that Broom (No. 9, p. 478) had previously stated his conclusion, 

 that "there is very strong evidence in favour of the homology of 

 the mammalian palatine process of the premaxillary with the so-called 

 'vomer' of at least the lizard and snake". Broom further says that 



