CHAPTER II. 



THE TEETH OF HESPERORNIS. 



(Plates I, II, and XX.) 



The absence of teetli has long been regarded as one of the best 

 distinctive characters of Birds; since teeth are present in some members of 

 all the other classes of vertebrates. All existing Birds have the jaws 

 covered with a homy sheath, which is usually smooth. In some groups, 

 this beak-covering is more or less serrated, and in a very few forms the 

 elevations correspond to slig-ht projections of the bone beneath, but no 

 indications of time teeth have yet been found. This may all be said like- 

 wise of existing Turtles. 



Geoffroy Saint-Hilaire and others have, indeed, detected in the young 

 of some recent birds vascular papillae which resembled those of embryonic 

 teeth ; but they were apparently portions of the undeveloped horny beak. 



The teeth of Hesperomis are true teeth, with their distinctive charac- 

 ters as well marked as those of any reptile. In the upper jaw, they are 

 confined to the maxillary bone alone, the premaxillary being entirely 

 edentulous. In the lower jaw, the teeth extend from very near the anterior 

 extremity of the ramus along the entire upper border of the dentary bone. 



The teeth above and below were implanted in a continuous groove, 

 somewhat like those of Ichthyosaurus. From the sides of the groove, 

 slight projections extend between the teeth, thus forming faint indications 

 of sockets ; but these projections are not sufficient to materially lessen the 

 width or depth of the groove. (Plate II, figure 11). 



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