THE TEETH OF BIRDS. 



The outer side of the crown is nearly flat, the inner strongly 

 convex : the junction of these surfaces is marked by a sharp 

 ridge, not serrated. 



In form the teeth of Hesperornis present a close resem- 

 blance to those of Mosasaurus, a great extinct lizard. 



Indeed, as Prof. Marsh observes, "in all their main 



features the teeth of Hesperornis are essentially reptilian, 

 and no anatomist would hesitate to refer them to that class, 

 had they been found alone. Combined with the other 

 reptilian characters of Hesperornis .... they clearly 

 indicate a genetic connection with that group." 



In the dentine contour lines are abundant ; the enamel 

 is so dense as to appear structureless, and there is no coronal 

 cementum. 



The foregoing account is condensed from the magnificent 

 volume published by the United States Government Geo- 

 logical Exploration. (Odontornithes, a monograph, &c., by 

 0. C. Marsh, Prof, of Palaeontology, Yale College.) 



With these notable exceptions, the jaws of all known birds 

 are toothless, the horny cases forming their beaks taking the 

 places and fulfilling the functions of teeth. 



(*) (After Prof Marsh. ) A. Hesperornis regalis, with successional tooth 

 in an excavation at its base ; enlarged eight diameters. B. Tooth of Mos- 

 asaurus princeps, half natural size. 



