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



corresponds with that part of the intermaxilla which lies between 

 the incisive canal and the mesial palatal suture." It would 

 appear from the descriptions thus summarised that Sir Wm. 

 Turner regards the dumb-bell bone as consisting merely of a pala- 

 tine plate, since he considers it to be fused along its mesial line 

 dorsally with the anterior end of the vomer. We shall see pre- 

 sently that the mesial bone rising dorsally, vomer-like, from the 

 palatine dumb-bell is an integral part of the bone itself, and is 

 quite distinct from the true vomer, which ends quite posteriorly 

 to this region. It may also be noted that what Turner has 

 regarded as fibrous membrane filling up the extensive hiatus in 

 the hard palate is in reality a thin sheet of hyaline cartilage 

 forming the floor of the nose, as was shown by Dr. C. J. Martin 

 and the writer in the paper already referred to (1). It is in this 

 cartilaginous layer, and not in fibrous membrane, that the dumb- 

 bell bone is imbedded. Owen and Meckel both refer to this car- 

 tilage forming the floor of the nose, and Meckel (2, p. 40) gives 

 its dimensions and attachments as seen from below. 



The additional observations of Professor Symington may now 

 be reviewed. He notes the close relation of the upper surface of 

 the anterior nodule of the dumb-bell " to the cartilages of the 

 nose which contain Jacobson's organ," and he further mentions 

 the fact, to which Martin and I have also drawn attention, that 

 near the posterior extremity of the dumb-bell it is covered, as seen 

 from below, by a thin layer of cartilage. As our figure shows, 

 however (1, PL xxiil. fig. 17), this is due to the hinder end being 

 more deeply embedded in the cartilaginous nasal floor and not 

 merely grafted upon its under surface as appears, superficially, to 

 be the case in front. From his study of coronal sections Syming- 

 ton has recognised that the bone projecting from the mesial dorsal 

 surface of the palatine dumb-bell is, as has been said above, an 

 integral part of that bone, and his description and figure (9, PI. 

 XLiil. 2) of a coronal section through the bone near the middle of 

 the posterior nodule will sufiice to carry conviction upon this 

 point. In such a section the bone appears *' as composed of two 

 crescents with their convexities directed inwards, and the greater 



