138 ON THE "dumb-bell-shaped" BONE IN ORNITHORHYNCHUS, 



erroneous view of the relation of the dumb-bell bone to the vomer. 

 This is an extremely important point, and I am surprised that 

 Prof. Symington does not explicitly recognise the mistake which 

 his observations were quite sufficient to correct. It is very plain, 

 both from Symington's observations and my own, that the dumb- 

 bell-shaped bone is not inferior but anterior to the vomer, and 

 that it is not " fused with the inferior border " of the latter. 



The criteria that remain, — viz,, that it " has no relation to the 

 anterior nares," that " it enters into the constitution of the hard 

 palate," and that " it forms the inner boundary of the entrance 

 into the naso-palatine canal " — may be sufficient to disprove the 

 homology to the prenasal bone of the pig. A powerful additional 

 argument against the homology to the prenasal bone in the pig is 

 derived from the observations of Dr. Martin and the writer upon 

 the anterior extension of the cartilaginous septum in Ornitho- 

 rhynchus in the form of a flattened 'prenasal plate' lying in front 

 of the dumb-bell bone and continuous behind with the ventral 

 extensions of the alinasal or aliseptal cartilages which form the 

 cartilaginous nasal floor (1, pp. 185-8). But the reasons adduced 

 do not appear to me sufficient to establish the intermaxillary natui-e 

 of the dumb-bell bone against the contention that that bone is a 

 true " anterior vomer " formed, of course, by the fusion of two 

 bilaterally symmetrical halves, and this is the view which it is 

 one of the objects of this paper to advocate. Whenever it is 

 recognised that the vertical bony lamella dorsad of the palatine 

 dumb-bell is not part of the vomer but an integral part of the 

 so-called dumb-bell bone, certain of the relations and connections of 

 that bone at once suggest difficulties in the way of its explanation 

 as premaxillary. 



(1) Although the palatine plate of the dumb-bell bone appears 

 at first sight as if it were situated in the same morphological 

 plane with the maxillary palate behind it, this is not really the 

 case, because the hinder end of the palatine dumb-bell is embedded 

 in and covered ventrally by the cartilage of the nasal floor, in 

 front of the maxillary palate. (See tigs. 1 & 9 ; and also Macleay 

 Memorial Vol. [1], PL xxin. fig. 17.) 



